Clean Code PHP

မာတိကာ

1. Introduction
2. Variables
   • Use meaningful and pronounceable variable names
   • Use the same vocabulary for the same type of variable
   • Use searchable names (part 1)
   • Use searchable names (part 2)
   • Use explanatory variables
   • Avoid nesting too deeply and return early (part 1)
   • Avoid nesting too deeply and return early (part 2)
   • Avoid Mental Mapping
   • Don't add unneeded context
   • Use default arguments instead of short circuiting or conditionals
3. Comparison
   • Use identical comparison
4. Functions
   • Function arguments (2 or fewer ideally)
   • Functions should do one thing
   • Function names should say what they do
   • Functions should only be one level of abstraction
   • Don't use flags as function parameters
   • Avoid Side Effects
   • Don't write to global functions
   • Don't use a Singleton pattern
   • Encapsulate conditionals
   • Avoid negative conditionals
   • Avoid conditionals
   • Avoid type-checking (part 1)
   • Avoid type-checking (part 2)
   • Remove dead code
5. Objects and Data Structures
   • Use object encapsulation
   • Make objects have private/protected members
6. Classes
   • Prefer composition over inheritance
   • Avoid fluent interfaces
   • Prefer final classes
7. SOLID
   • Single Responsibility Principle (SRP)
   • Open/Closed Principle (OCP)
   • Liskov Substitution Principle (LSP)
   • Interface Segregation Principle (ISP)
   • Dependency Inversion Principle (DIP)
8. Don’t repeat yourself (DRY)
9. Translations

နိဒါန်း

Robert C. Martin ရဲ့ လက်ရာမြှောက် Clean Code စာအုပ်ထဲက Software engineering principles တွေကို PHP Language အတွက် သီးသန့် (ဆီလျှော်အောင်) ပြန်လည်မွမ်းမံ စုစည်းပေးထားတာ ဖြစ်ပါတယ်။ ဒါက Coding Style Guideline တစ်ခု မဟုတ်ပါဘူး။ PHP program တွေရေးတဲ့အခါ

• Code တွေ ရှင်းရှင်းလင်းလင်းဖြစ်အောင် (ဝါ) readable ဖြစ်အောင် ၊
• Code အစိတ်အပိုင်းများကို တခါရေးပြီးနောက် အခြားနေရာများတွင်လည်း ပြန်လည်အသုံးချနိုင်အောင် (ဝါ) reusable ဖြစ်အောင်၊
• ရှုပ်ထွေးနေတဲ့ Code တွေကို လိုအပ်ရင် အလွယ်တကူ သပ်သပ်ရပ်ရပ် Structure ကျကျ ပြန်လည်ပြင်ဆင်နိုင်တဲ့ (ဝါ) refactorable ဖြစ်အောင်

ရေးသားနိုင်ဖို့ အကူအညီပေးမယ့် လမ်းညွှန်ချက်တစ်ခုဆိုရင် ပိုမှန်ပါလိမ့်မယ်။

ဒီမှာဖော်ပြထားတဲ့ Software ရေးသားနည်း ဥပဒေသတွေကို တသွေမတိမ်း လိုက်နာဖို့တော့ မလိုအပ်ပါဘူး။ တကယ်ဆိုရင် တချို့သော ဥပဒေသတွေကိုသာ နေရာတိုင်းမှာ မှန်တယ်လို့ လက်ခံထားကြတာပါ။ အများစုက သူ့နေရာနဲ့သူ မှန်ကန်အောင် အသုံးချတတ်မှသာ အသုံးဝင်မှာပါ။ ဒီ ဥပဒေသတွေက လမ်းညွှန်တစ်ခုထက် မပိုပါဘူး။ ဒါပေမယ့် ဒီလမ်းညွှန်ချက်တွေက နှစ်ပေါင်းများစွာ code တွေရေးရင်း ရလာတဲ့ အတွေအကြုံတွေကို Clean Code ရဲ့ မူရင်းရေးသားသူက ကြိုးစားပြီး စုစည်းပေးထားတာပါ။

Inspired from clean-code-javascript.

အခုလက်ရှိ PHP developers တော်တော်များများက PHP 5 ကို သုံးနေဆဲဖြစ်ပေမယ့်၊ Code example တော်တော်များများကိုတော့ PHP 7.1+ သာ စမ်းကြည့်လို့ ရမှာဖြစ်ပါတယ်။

Variables

Use meaningful and pronounceable variable names

Variable တွေနာမည်ပေးတဲ့အခါ ထင်ရှားတဲ့ အဓိပ္ပာယ်ရှိပြီး အသံထွက်ဖတ်လို့ရတဲ့ စကားလုံးမျိုးတွေကိုသာ ရွေးချယ်သင့်ပါတယ်။

မဖြစ်သင့်:

$ymdstr = $moment->format('y-m-d');

ဖြစ်သင့်:

$currentDate = $moment->format('y-m-d');

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Use the same vocabulary for the same type of variable

အမျိုးအစားတူတဲ့ variable တွေအတွက် နာမည်ပေးတဲ့အခါ တူညီတဲ့ ဝေါဟာရတခုတည်းကိုသာ တသတ်မတ်တည်း အသုံးပြုသင့်ပါတယ်။

မဖြစ်သင့်:

getUserInfo();
getUserData();
getUserRecord();
getUserProfile();

ဖြစ်သင့်:

getUser();

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Use searchable names (part 1)

ကျွန်တော်တို့ Programmer တွေဟာ Code ရေးလို့ အချိန်ကုန်တာထက်စာရင် ရေးပြီးသား Code ကို နားလည်အောင်ပြန်ဖတ်ရတာအတွက် အချိန်ပိုကုန်လေ့ ရှိပါတယ်။ ဒါကြောင့် ကျွန်တော်တို့ ရေးတဲ့ Code တွေဟာ ပြန်ဖတ်တဲ့အခါ ဖတ်ရလွယ်ကူဖို့နဲ့ လွယ်လင့်တကူပြန်ရှာလို့ရနိုင်ဖို့ အရေးကြီးလှပါတယ်။

ပြန်ရှာတယ်ဆိုတာ - ဥပမာ: Code Line ပေါင်း ၁၀၀၀၀ လောက် ရှိတဲ့ Project ကြီးမှာ User Log In စဝင်တဲ့ အချိန်ကို ဘယ် Variable နဲ့ မှတ်ထားမိလဲဆိုတာ ပြန်ရှာသလိုမျိုးပေါ့။ userLogInTime လို့ variable ကို နာမည်မပေးဘဲ uLInTime လို့ အတိုကောက် ပေးလိုက်ရင် နောက် Maintain လုပ်မယ့် Developer အနေနဲ့ နားလည်ဖို့ အခက်အခဲဖြစ်သွားနိုင်တာကို ဆိုလိုတာပါ။

ဒါကြောင့် variable နာမည်ပေးတဲ့အခါ ပြီးပြီးရောမပေးသင့်ပါဘူး။ ကိုယ်ရေးနေတဲ့ program ကို ပြန်ဖတ်တဲ့အခါ နားလည်လွယ်စေဖို့ ရည်ရွယ်ပြီး သေချာရွေးချယ်ပြီးမှ ပေးသင့်ပါတယ်။ အဲလိုမှ မဟုတ်ရင် ကိုယ့် program ကို ဖတ်မယ့်သူတွေကို အခက်အခဲ များစွာ ဖြစ်ပေါ်စေမှာပါ။ လိုရင်းကတော့ variable နာမည်ကို ပြန်ဖတ်ရင် အဓိပ္ပာယ်ရှိအောင်၊ ပြန်ရှာလို့လွယ်အောင် ပေးပါ။

မဖြစ်သင့်:

// 448 ဆိုတာ ဘာကြီးလဲ၊ ဘာကိုဆိုလိုတာလဲ
$result = $serializer->serialize($data, 448);

ဖြစ်သင့်:

$json = $serializer->serialize($data, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE);

Use searchable names (part 2)

မဖြစ်သင့်::

// 4 ဆိုတာ ဘာကြီးလဲ၊ ဘာကိုရည်ရွယ်ခြင်တာလဲ
if ($user->access & 4) {
    // ...
}

ဖြစ်သင့်:

class User
{
    const ACCESS_READ = 1;
    const ACCESS_CREATE = 2;
    const ACCESS_UPDATE = 4;
    const ACCESS_DELETE = 8;
}

if ($user->access & User::ACCESS_UPDATE) {
    // do edit ...
}

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Use explanatory variables

Variable တွေကို အဓိပ္ပာယ်ပေါ်အောင် နာမည်ကောင်းကောင်း ပေးတတ်ရုံနဲ့ မလုံလောက်သေးပါဘူး။ Variable ကို အသုံးပြုမယ့် scope နဲ့ code statement ပေါ်မူတည်ပြီး မှန်ကန်အောင် ရေးတတ်ရပါသေးတယ်။ Technically အရ Scope in mind လို့ ခေါ်ပါတယ်။

Variable ကို အသုံးပြုထားတဲ့ code statement ကို ကြည့်ရုံနဲ့ variable ထဲမှာ ဘာ data သိမ်းပြီး process လုပ်သွားတာလဲ၊ ဘာ ရည်ရွယ်ချက်နဲ့ code statement မှာ သုံးသွားလဲဆိုတဲ့ အဓိပ္ပာယ်ပေါ်အောင်လည်း ရေးတတ်ရပါတယ်။

မဖြစ်သင့်:

အောက်ပါ ဥပမာမှာဆို regular expression ကို process လုပ်သွားတဲ့ preg_match function ထဲမှာ ပေးထားတဲ့ $matches ဆိုတဲ့ variable ဟာ သူ အဓိပ္ပာယ်နဲ့သူ မှန်နေပါတယ်။

ဒါပေမယ့် saveCityZipCode function မှာ parameters အနေနဲ့ပေးတဲ့အခါကျတော့ $matches[1], $matches[2] လို့ ပေးလိုက်တာဟာ code statement ကို ဖတ်ရတာ ဝေဝါးသွားစေပါတယ်။ $matches[1] ဆိုတာ $matches ဆိုတဲ့ array ရဲ့ ပထမအခန်းကို ရည်ညွှန်းမှန်းသိပေမယ့် အဲ့ဒီ ပထမအခန်းထဲမှာ ဘာ data သိမ်းထားမှန်းဆိုတာကတော့ မသိရတော့ပါဘူး။ အဲဒီတော့ code ကို maintain လုပ်မယ့်သူက အပေါ်က regular expression ကို အသေးစိတ်နားလည်အောင် သွားဖတ်ရပါတော့မယ်။

$address = 'One Infinite Loop, Cupertino 95014';
$cityZipCodeRegex = '/^[^,]+,\s*(.+?)\s*(\d{5})$/';
preg_match($cityZipCodeRegex, $address, $matches);

saveCityZipCode($matches[1], $matches[2]);

အသင့်အတင့်:

အောက်က ပိုမိုကောင်းမွန်အောင် ပြန်လည်ပြင်ဆင်ထားတဲ့ ဥပမာကို ကြည့်ပါဦး။

ဒီဥပမာမှာတော့ saveCityZipCode function ရေးသားပုံက ကောင်းမွန်သွားပါပြီ။ ဒါပေသိ [, $city, $zipCode] = $matches ဆိုတဲ့ code line ဟာ code နားလည်လွယ်အောင် အပိုရေးလိုက်ရတဲ့ code တစ်ကြောင်းပုံစံ ဖြစ်သွားပါတယ်။ တကယ့် ရှုပ်ထွေးမှုတွေကို ဖြစ်ပေါ်စေတဲ့ regular expression ကို မရှင်းဘဲ code အပိုတစ်ကြောင်း ရေးလိုက်သလို ဖြစ်သွားတာပါ။

စာခြွင်း။ ။ တကယ့်လက်တွေ့မှာတော့ ဒီဥပမာက code ရေးသားမှုပုံစံဟာ လက်သင့်ခံလို့ ရပါတယ်။ အခုလောက် ရှင်းလင်းသပ်ရပ်မှု ရှိပြီဆိုရင် မဆိုးဘူးလို့ ပြောလို့ရပါပြီ။ ဘာဖြစ်လို့လဲဆိုရင် တကယ်လက်တွေ့ Project တွေမှာက အချိန်ဒီလောက် မပေးပါဘူး။ refactoring လုပ်ရင်း feature အသစ်ရေးရမယ့် အချိန်တွေပါ ကုန်သွားမှာကိုလည်း ဆင်ခြင်သင့်ပါတယ်။

$address = 'One Infinite Loop, Cupertino 95014';
$cityZipCodeRegex = '/^[^,]+,\s*(.+?)\s*(\d{5})$/';
preg_match($cityZipCodeRegex, $address, $matches);

[, $city, $zipCode] = $matches;
saveCityZipCode($city, $zipCode);

ဖြစ်သင့်:

အခု ဥပမာမှာတော့ code ရေးသားမှုဟာ အကောင်းဆုံးပုံစံကို ရောက်ရှိသွားပြီလို့ ယူဆလို့ ရပါတယ်။ တကယ့် ရှုပ်ထွေးမှုကို ဖြစ်စေတဲ့ regular expression ကို ရှင်းလင်းအောင် subpattern တွေကို (naming) နာမည်ပေးပြီး ဖြေရှင်းလိုက်နိုင်ပါတယ်။ code ရေးသားမှုမှာလည်း အပိုအလို မရှိ ကျစ်လစ်သွားပါတယ်။

$address = 'One Infinite Loop, Cupertino 95014';
$cityZipCodeRegex = '/^[^,]+,\s*(?<city>.+?)\s*(?<zipCode>\d{5})$/';
preg_match($cityZipCodeRegex, $address, $matches);

saveCityZipCode($matches['city'], $matches['zipCode']);

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Avoid nesting too deeply and return early (part 1)

Nested if-else statement တွေကို တတ်နိုင်သလောက် ရှောင်ပါ။ return statement တွေ အများကြီး ပြန်တာမျိုးတွေကိုလည်း ရှောင်ပါ။ (အပိုင်း ၁)

if-else statement တွေ သိပ်များသွားရင် code ကို trace လိုက်ရတာ ခက်ခဲသွားစေပါတယ်။ နောက်တစ်ခု ယူဆလို့ ရတာက ကိုယ့် ရေးတဲ့ function ထဲမှာ if-else statement တွေ ၂ ခု ၃ ခုထက် ပိုနေပြီဆိုရင် ကိုယ့် function က အလုပ်တစ်ခုထက် မက လုပ်နေပြီလို့ ယူဆလို့ ရပါတယ်။ function တစ်ခုက လုပ်ဆောင်ချက် တစ်ခုဘဲ ရှိသင့်ပါတယ်။ ဒီလို အခါမျိုးမှာ Polymorphism (သို့) State/Strategy pattern နဲ့ ပြန်ပြီး code ကို refactor လုပ်လို့ ရပါတယ်။

function တစ်ခုကနေ return statement တွေ အများကြီး ပြန်တာမျိုးတွေကိုလည်း ရှောင်သင့်ပါတယ်။ ဒီအချက်ကလည်း function တစ်ခုကို trace လိုက်ရတာ အတော်လေး ခက်ခဲသွားစေနိုင်တဲ့ အချက်ပါ။ return statement အများဆုံး ဘယ်လောက်ဘဲ ရှိသင့်တယ်လို့တော့ အတိအကျ သတ်မှတ်ထားတာ မရှိပါဘူး။ နည်းနိုင်သမျှ နည်းတာတော့ ကောင်းပါတယ်။

Returning early ဆိုတဲ့ အယူအဆ မျိုးတော့ ရှိပါတယ်။ ဥပမာ - file download လုပ်တဲ့ function တစ်ခုမှာ Internet connection မရှိရင် exception တက်တာဘဲဖြစ်ဖြစ်၊ return false ပြန်တာဘဲဖြစ်ဖြစ်ကို function ရဲ့ အပေါ်ဆုံး code line တွေမှာ ရေးလို့ ရပါတယ်။ ဒါပေမယ့် function ကို ဖတ်ရတာ ပိုကောင်းသွားစေတယ်လို့ သေချာမှသာ ဒီလိုမျိုး ရေးသင့်ပါတယ်။

စာခြွင်း ရှင်းလင်းချက်: trace လိုက်တယ်ဆိုတာ code တကြောင်းခြင်းစီက ဘာအလုပ်လုပ်သွားလဲ၊ ဘာ output ထွက်သွားလဲဆိုတာ လိုက်ကြည့်တယ်လို့ ယေဘုယျနားလည်လို့ ရပါတယ်။ PHP မှာဆိုရင် xdebug နဲ့ debug လိုက်ကြည့်သလိုမျိုး၊ var_dump နဲ့ print ထုတ်ကြည့်သလိုမျိုးပေါ့။ ဒီလို tools တွေနဲ့ မဟုတ်ဘဲ စိတ်ထဲမှာဘဲဖြစ်စေ၊ စာအုပ်ပေါ်မှာ ချရေးပြီးတော့ ဖြစ်စေ step by step စိတ်မှန်းနဲ့လည်း trace လိုက်သွားတာမျိုးလည်း ရှိပါတယ်။ အဲဒါကို term အရ Dry Run လို့ ခေါ်ပါတယ်။

ပုံမှန် trace ကို code ရဲ့ ဘယ်နားက error တက်သွားလဲဆိုတာသိဖို့ လိုက်ကြတာ များပါတယ်။ သို့မဟုတ် သူများရေးထားတဲ့ (ကိုယ်အရင်က ရေးထားပေမယ့် မေ့သွားတဲ့) code တွေကို နားလည်အောင် ပြန် ဖတ်တဲ့ အခါမျိုးမှာလည်း သုံးပါတယ်။

မဖြစ်သင့်:

function isShopOpen($day): bool
{
    if ($day) {
        if (is_string($day)) {
            $day = strtolower($day);
            if ($day === 'friday') {
                return true;
            } elseif ($day === 'saturday') {
                return true;
            } elseif ($day === 'sunday') {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    } else {
        return false;
    }
}

ဖြစ်သင့်:

function isShopOpen(string $day): bool
{
    if (empty($day)) {
        return false;
    }

    $openingDays = [
        'friday', 'saturday', 'sunday'
    ];

    return in_array(strtolower($day), $openingDays, true);
}

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Avoid nesting too deeply and return early (part 2)

မဖြစ်သင့်:

function fibonacci(int $n)
{
    if ($n < 50) {
        if ($n !== 0) {
            if ($n !== 1) {
                return fibonacci($n - 1) + fibonacci($n - 2);
            } else {
                return 1;
            }
        } else {
            return 0;
        }
    } else {
        return 'Not supported';
    }
}

ဖြစ်သင့်:

function fibonacci(int $n): int
{
    if ($n === 0 || $n === 1) {
        return $n;
    }

    if ($n > 50) {
        throw new \Exception('Not supported');
    }

    return fibonacci($n - 1) + fibonacci($n - 2);
}

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Avoid Mental Mapping

ဒီအချက်ကတော့ အပေါ်ကအချက်တွေကိုဘဲ မူကွဲပုံစံ တစ်မျိုးနဲ့ ပြောထားတာပါ။ Variable တစ်ခုကို နားလည်ဖို့ သူ့ထဲမှာ သိမ်းထားတဲ့ data ကို သွားဖတ်ပြီးမှ သိရတာမျိုးက မကောင်းပါဘူး။ ရှင်းလင်းပြတ်သားခြင်းက သွယ်ဝိုက်နေတာထက် ပိုကောင်းပါတယ်။

မဖြစ်သင့်:

$l = ['Austin', 'New York', 'San Francisco'];

for ($i = 0; $i < count($l); $i++) {
    $li = $l[$i];
    doStuff();
    doSomeOtherStuff();
    // ...
    // ...
    // ...
    // Wait, what is `$li` for again?
    dispatch($li);
}

ဖြစ်သင့်:

$locations = ['Austin', 'New York', 'San Francisco'];

foreach ($locations as $location) {
    doStuff();
    doSomeOtherStuff();
    // ...
    // ...
    // ...
    dispatch($location);
}

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Don't add unneeded context

ဖော်ပြခဲ့သမျှ အချက်တွေကတော့ Variable နာမည် ပေးတဲ့အခါ တတ်နိုင်သမျှ ပြည့်စုံရှင်းလင်းအောင် ရေးဖို့ ပြောထားတာပါ။ ဒါပေမယ့် မလိုအပ်ဘဲ စကားဆက် (context) တွေ မထည့်မိဖို့လည်း အရေးကြီးပါတယ်။

ဥပမာပေးရမယ်ဆိုရင် class/object ထဲက member variable တိုင်းမှာ class နာမည်ကြီးကို ရှေ့က လိုက်ထည့်နေတာမျိုးပါ။ "User" class ထဲမှာ user ရဲ့ အသက်ကိုသိမ်းဖို့ variable ကို နာမည်ပေးတဲ့အခါ age ဆိုရင် လုံလောက်ပါပြီ။ userAge ဆိုပြီး စကားဆက် (context) ကို ရှေ့ကခံပေးစရာ မလိုပါဘူး။ ဘာဖြစ်လို့လဲဆိုရင်အဲ့ဒီ age ဆိုတဲ့ member variable ကို ခေါ်သုံးတဲ့အခါ user->age ဆိုပြီး ခေါ်သုံးရမှာ ဖြစ်လို့ပါ။ user->age ဆိုတဲ့ code expression ကို ကြည့်မယ်ဆိုရင် user ရဲ့ age ကို ရည်ညွှန်းမှန်း သိသာပါတယ်။

မဖြစ်သင့်:

class Car
{
    public $carMake;
    public $carModel;
    public $carColor;

    //...
}

ဖြစ်သင့်:

class Car
{
    public $make;
    public $model;
    public $color;

    //...
}

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Use default arguments instead of short circuiting or conditionals

Programmer တွေအနေနဲ့ Function တွေကို ရေးတဲ့အခါတိုင်း parameter declaration ဆိုတာကို တနည်းမဟုတ်တနည်းနဲ့တော့ ကြုံကြရတာပါဘဲ။

Parameter ကြေငြာတဲ့အခါ အဲဒီ parameter အတွက် default value သတ်မှတ်ပေးဖို့ လိုအပ်တဲ့အခါတိုင်း default argument ကြေငြာတဲ့ပုံစံမျိုးနဲ့ဘဲ ရေးသင့်ပါတယ်။ Ternary conditional ပုံစံတွေ၊ short circuiting ပုံစံတွေနဲ့ မရေးသင့်ပါဘူး။

စာခြွင်း။ ။ short circuiting ဆိုတဲ့ term က တချို့သော developer တွေအတွက် အနည်းငယ် စိမ်းနေနိုင်ပါတယ်။ ဒီ wiki link နဲ့ stackoverflow link မှာတော့ ရှင်းထားတာ အတော်လေး ကောင်းပါတယ်။

မဖြစ်သင့်:

ဒီရေးသားမှုပုံစံဟာ လိုအပ်ချက်ရှိနေသေးတယ်လို့ ယူဆလို့ရပါတယ်။ အောက်ပါ function ကိုသာ $this->createMicrobrewery(null) နဲ့ call လိုက်ရင် $breweryName ဟာ ဖြစ်စေခြင်တဲ့ default value “Hipster Brew Co.” အစား null value ဝင်သွားမှာပါ။

စာခြွင်း။ ။ ကိုယ်ပိုင်အမြင်အရဆိုရင် ဒီရေးသားမှုပုံစံဟာ function ရဲ့ argument control ကို လျှော့ကျသွားတယ် ဆိုရုံလောက်ဘဲ ယူဆလို့ ရတာပါ။ PHP လို dynamic typing language တစ်ခုမှာ function parameter တစ်ခုကို null value ဝင်တာနဲ့ မကောင်းဘူးပြောဖို့ဆိုတာ အနည်းငယ် တဖက်သက်ဆန်တယ်လို့ ခံစားမိပါတယ်။

function createMicrobrewery($breweryName = 'Hipster Brew Co.'): void
{
    // ...
}

အသင့်အတင့်:

ဒီရေးသားမှုပုံစံကတော့ မဆိုးဘူးလို့ ပြောလို့ရပါပြီ။ default value ကို null လို့ ထားလိုက်တယ်။ ပြီးမှ function body ထဲမှာ ternary operator နဲ့ null ဖြစ်ခဲ့ရင် actual default value “Hipster Brew Co.” ထည့်မယ်ဆိုပြီး ရေးလိုက်ပါတယ်။

ဒါကြောင့် argument မသတ်မှတ်ဘဲ function call လိုက်သည်ဖြစ်စေ၊ null or empty value ပေးလိုက်သည်ဖြစ်စေ $breweryName parameter ဟာ actual default value “Hipster Brew Co.” ရှိနေတော့မှာပါ။

စာခြွင်း။ ။ ဒီ ရေးသားမှုမှာလည်း မိမိကိုယ်ပိုင်အမြင်အရဆိုရင် အရမ်းကြီး သဘောမတူခြင်ပါဘူး။ default argument ဆိုတာ null value ကို ရှောင်ခြင်လို့ ရေးရတာမျိုး မဟုတ်ပါဘူး။ function call တဲ့ အချိန်မှာ လိုအပ်တဲ့ parameter အတွက် argument မပေးခဲ့ဘူးဆိုရင် logic အရ default value တစ်ခု သတ်မှတ်ပေးလိုက်တဲ့ သဘောပါ။

function createMicrobrewery($name = null): void
{
    $breweryName = $name ?: 'Hipster Brew Co.';
    // ...
}

ဖြစ်သင့်:

ဒီ ရေးသားမှုမှာတော့ Php7 ရဲ့ type hinting feature ကို အသုံးပြုပြီး argument ကို string datatype နဲ့ restrict လုပ်လိုက်ပါတယ်။ ဒါကြောင့် null value ဝင်လာခဲ့ရင် exception တက်မှာပါ။

null value ဖြစ်မှာလည်း စိုးရိမ်စရာ မလိုတော့သလို default argument လည်း ကြေငြာပြီးသား ဖြစ်သွားစေတဲ့အတွက် ကောင်းမွန်တဲ့ ရေးသားမှုတစ်ခုလို့ ဆိုလို့ရပါတယ်။

function createMicrobrewery(string $breweryName = 'Hipster Brew Co.'): void
{
    // ...
}

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Comparison

Use identical comparison

Php မှာ == (equality) နဲ့ === (identical) ဆိုပြီး comparison operator နှစ်မျိုးရှိတာ developer တိုင်း သိကြမှာပါ။ == (equality) comparison နဲ့ condition စစ်ရင် operands တွေကို type juggling လုပ်ပြီး === (identical) မှာတော့ မလုပ်ပါဘူး။

Type juggling rules အသေးစိတ်ကိုတော့ php official documentation မှာ သွားဖတ်လို့ ရပါတယ်။

Type juggling လုပ်တဲ့ rules တွေက အနည်းငယ် ရှုပ်ထွေးပြီး အလွတ်မှတ်ထား နိုင်ဖို့လည်း မလွယ်လှပါဘူး။ ဒါကြောင့် == (equality) operator နဲ့ရေးတဲ့ comparison expression တွေမှာ ကိုယ်မမျှော်လင့်ထားတဲ့ result တွေ ထွက်လာနိုင်ပါတယ်။

ဖြစ်နိုင်ရင်တော့ condition စစ်တိုင်း (===) identical comparison operator ကိုသာ သုံးသင့်ပါတယ်။

မဖြစ်သင့်:

အောက်ပါ code block မှာဆိုရင် (==) equality comparison operator က string ကို integer ပြောင်းလိုက်ပါတယ်။

$a = '42';
$b = 42;

if ($a != $b) {
   // The expression will always pass
}

string 42 နဲ့ integer 42 ဟာ computational logic အရ ဆိုရင် မတူပါဘူး။ ဒါပေမယ့် $a != $b လို့ comparison လုပ်လိုက်ရင်တော့ FALSE return ပြန်လာတာကို တွေ့ရမှာပါ။

ဖြစ်သင့်:

(===) identical operator ကတော့ operand တွေရဲ့ datatype မတူရင် value comparison ကို မလုပ်ဆောင်တော့ပါဘူး။

$a = '42';
$b = 42;

if ($a !== $b) {
    // The expression is verified
}

အထက်ပါ code block မှာတော့ မျှော်လင့်ထားတဲ့အတိုင်း TRUE ကို ရရှိမှာဘဲ ဖြစ်ပါတယ်။

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Functions

Function arguments (2 or fewer ideally)

Limiting the amount of function parameters is incredibly important because it makes testing your function easier. Having more than three leads to a combinatorial explosion where you have to test tons of different cases with each separate argument.

Zero arguments is the ideal case. One or two arguments is ok, and three should be avoided. Anything more than that should be consolidated. Usually, if you have more than two arguments then your function is trying to do too much. In cases where it's not, most of the time a higher-level object will suffice as an argument.

Bad:

function createMenu(string $title, string $body, string $buttonText, bool $cancellable): void
{
    // ...
}

Good:

class MenuConfig
{
    public $title;
    public $body;
    public $buttonText;
    public $cancellable = false;
}

$config = new MenuConfig();
$config->title = 'Foo';
$config->body = 'Bar';
$config->buttonText = 'Baz';
$config->cancellable = true;

function createMenu(MenuConfig $config): void
{
    // ...
}

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Functions should do one thing

This is by far the most important rule in software engineering. When functions do more than one thing, they are harder to compose, test, and reason about. When you can isolate a function to just one action, they can be refactored easily and your code will read much cleaner. If you take nothing else away from this guide other than this, you'll be ahead of many developers.

Bad:

function emailClients(array $clients): void
{
    foreach ($clients as $client) {
        $clientRecord = $db->find($client);
        if ($clientRecord->isActive()) {
            email($client);
        }
    }
}

Good:

function emailClients(array $clients): void
{
    $activeClients = activeClients($clients);
    array_walk($activeClients, 'email');
}

function activeClients(array $clients): array
{
    return array_filter($clients, 'isClientActive');
}

function isClientActive(int $client): bool
{
    $clientRecord = $db->find($client);

    return $clientRecord->isActive();
}

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Function names should say what they do

Bad:

class Email
{
    //...

    public function handle(): void
    {
        mail($this->to, $this->subject, $this->body);
    }
}

$message = new Email(...);
// What is this? A handle for the message? Are we writing to a file now?
$message->handle();

Good:

class Email 
{
    //...

    public function send(): void
    {
        mail($this->to, $this->subject, $this->body);
    }
}

$message = new Email(...);
// Clear and obvious
$message->send();

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Functions should only be one level of abstraction

When you have more than one level of abstraction your function is usually doing too much. Splitting up functions leads to reusability and easier testing.

Bad:

function parseBetterJSAlternative(string $code): void
{
    $regexes = [
        // ...
    ];

    $statements = explode(' ', $code);
    $tokens = [];
    foreach ($regexes as $regex) {
        foreach ($statements as $statement) {
            // ...
        }
    }

    $ast = [];
    foreach ($tokens as $token) {
        // lex...
    }

    foreach ($ast as $node) {
        // parse...
    }
}

Bad too:

We have carried out some of the functionality, but the parseBetterJSAlternative() function is still very complex and not testable.

function tokenize(string $code): array
{
    $regexes = [
        // ...
    ];

    $statements = explode(' ', $code);
    $tokens = [];
    foreach ($regexes as $regex) {
        foreach ($statements as $statement) {
            $tokens[] = /* ... */;
        }
    }

    return $tokens;
}

function lexer(array $tokens): array
{
    $ast = [];
    foreach ($tokens as $token) {
        $ast[] = /* ... */;
    }

    return $ast;
}

function parseBetterJSAlternative(string $code): void
{
    $tokens = tokenize($code);
    $ast = lexer($tokens);
    foreach ($ast as $node) {
        // parse...
    }
}

Good:

The best solution is move out the dependencies of parseBetterJSAlternative() function.

class Tokenizer
{
    public function tokenize(string $code): array
    {
        $regexes = [
            // ...
        ];

        $statements = explode(' ', $code);
        $tokens = [];
        foreach ($regexes as $regex) {
            foreach ($statements as $statement) {
                $tokens[] = /* ... */;
            }
        }

        return $tokens;
    }
}

class Lexer
{
    public function lexify(array $tokens): array
    {
        $ast = [];
        foreach ($tokens as $token) {
            $ast[] = /* ... */;
        }

        return $ast;
    }
}

class BetterJSAlternative
{
    private $tokenizer;
    private $lexer;

    public function __construct(Tokenizer $tokenizer, Lexer $lexer)
    {
        $this->tokenizer = $tokenizer;
        $this->lexer = $lexer;
    }

    public function parse(string $code): void
    {
        $tokens = $this->tokenizer->tokenize($code);
        $ast = $this->lexer->lexify($tokens);
        foreach ($ast as $node) {
            // parse...
        }
    }
}

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Don't use flags as function parameters

Flags tell your user that this function does more than one thing. Functions should do one thing. Split out your functions if they are following different code paths based on a boolean.

Bad:

function createFile(string $name, bool $temp = false): void
{
    if ($temp) {
        touch('./temp/'.$name);
    } else {
        touch($name);
    }
}

Good:

function createFile(string $name): void
{
    touch($name);
}

function createTempFile(string $name): void
{
    touch('./temp/'.$name);
}

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Avoid Side Effects

A function produces a side effect if it does anything other than take a value in and return another value or values. A side effect could be writing to a file, modifying some global variable, or accidentally wiring all your money to a stranger.

Now, you do need to have side effects in a program on occasion. Like the previous example, you might need to write to a file. What you want to do is to centralize where you are doing this. Don't have several functions and classes that write to a particular file. Have one service that does it. One and only one.

The main point is to avoid common pitfalls like sharing state between objects without any structure, using mutable data types that can be written to by anything, and not centralizing where your side effects occur. If you can do this, you will be happier than the vast majority of other programmers.

Bad:

// Global variable referenced by following function.
// If we had another function that used this name, now it'd be an array and it could break it.
$name = 'Ryan McDermott';

function splitIntoFirstAndLastName(): void
{
    global $name;

    $name = explode(' ', $name);
}

splitIntoFirstAndLastName();

var_dump($name); // ['Ryan', 'McDermott'];

Good:

function splitIntoFirstAndLastName(string $name): array
{
    return explode(' ', $name);
}

$name = 'Ryan McDermott';
$newName = splitIntoFirstAndLastName($name);

var_dump($name); // 'Ryan McDermott';
var_dump($newName); // ['Ryan', 'McDermott'];

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Don't write to global functions

Polluting globals is a bad practice in many languages because you could clash with another library and the user of your API would be none-the-wiser until they get an exception in production. Let's think about an example: what if you wanted to have configuration array? You could write global function like config(), but it could clash with another library that tried to do the same thing.

Bad:

function config(): array
{
    return  [
        'foo' => 'bar',
    ]
}

Good:

class Configuration
{
    private $configuration = [];

    public function __construct(array $configuration)
    {
        $this->configuration = $configuration;
    }

    public function get(string $key): ?string
    {
        return isset($this->configuration[$key]) ? $this->configuration[$key] : null;
    }
}

Load configuration and create instance of Configuration class

$configuration = new Configuration([
    'foo' => 'bar',
]);

And now you must use instance of Configuration in your application.

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Don't use a Singleton pattern

Singleton is an anti-pattern. Paraphrased from Brian Button:

1. They are generally used as a global instance, why is that so bad? Because you hide the dependencies of your application in your code, instead of exposing them through the interfaces. Making something global to avoid passing it around is a code smell.
2. They violate the single responsibility principle: by virtue of the fact that they control their own creation and lifecycle.
3. They inherently cause code to be tightly coupled. This makes faking them out under test rather difficult in many cases.
4. They carry state around for the lifetime of the application. Another hit to testing since you can end up with a situation where tests need to be ordered which is a big no for unit tests. Why? Because each unit test should be independent from the other.

There is also very good thoughts by Misko Hevery about the root of problem.

Bad:

class DBConnection
{
    private static $instance;

    private function __construct(string $dsn)
    {
        // ...
    }

    public static function getInstance(): DBConnection
    {
        if (self::$instance === null) {
            self::$instance = new self();
        }

        return self::$instance;
    }

    // ...
}

$singleton = DBConnection::getInstance();

Good:

class DBConnection
{
    public function __construct(string $dsn)
    {
        // ...
    }

     // ...
}

Create instance of DBConnection class and configure it with DSN.

$connection = new DBConnection($dsn);

And now you must use instance of DBConnection in your application.

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Encapsulate conditionals

Bad:

if ($article->state === 'published') {
    // ...
}

Good:

if ($article->isPublished()) {
    // ...
}

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Avoid negative conditionals

Bad:

function isDOMNodeNotPresent(\DOMNode $node): bool
{
    // ...
}

if (!isDOMNodeNotPresent($node))
{
    // ...
}

Good:

function isDOMNodePresent(\DOMNode $node): bool
{
    // ...
}

if (isDOMNodePresent($node)) {
    // ...
}

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Avoid conditionals

This seems like an impossible task. Upon first hearing this, most people say, "how am I supposed to do anything without an if statement?" The answer is that you can use polymorphism to achieve the same task in many cases. The second question is usually, "well that's great but why would I want to do that?" The answer is a previous clean code concept we learned: a function should only do one thing. When you have classes and functions that have if statements, you are telling your user that your function does more than one thing. Remember, just do one thing.

Bad:

class Airplane
{
    // ...

    public function getCruisingAltitude(): int
    {
        switch ($this->type) {
            case '777':
                return $this->getMaxAltitude() - $this->getPassengerCount();
            case 'Air Force One':
                return $this->getMaxAltitude();
            case 'Cessna':
                return $this->getMaxAltitude() - $this->getFuelExpenditure();
        }
    }
}

Good:

interface Airplane
{
    // ...

    public function getCruisingAltitude(): int;
}

class Boeing777 implements Airplane
{
    // ...

    public function getCruisingAltitude(): int
    {
        return $this->getMaxAltitude() - $this->getPassengerCount();
    }
}

class AirForceOne implements Airplane
{
    // ...

    public function getCruisingAltitude(): int
    {
        return $this->getMaxAltitude();
    }
}

class Cessna implements Airplane
{
    // ...

    public function getCruisingAltitude(): int
    {
        return $this->getMaxAltitude() - $this->getFuelExpenditure();
    }
}

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Avoid type-checking (part 1)

PHP is untyped, which means your functions can take any type of argument. Sometimes you are bitten by this freedom and it becomes tempting to do type-checking in your functions. There are many ways to avoid having to do this. The first thing to consider is consistent APIs.

Bad:

function travelToTexas($vehicle): void
{
    if ($vehicle instanceof Bicycle) {
        $vehicle->pedalTo(new Location('texas'));
    } elseif ($vehicle instanceof Car) {
        $vehicle->driveTo(new Location('texas'));
    }
}

Good:

function travelToTexas(Traveler $vehicle): void
{
    $vehicle->travelTo(new Location('texas'));
}

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Avoid type-checking (part 2)

If you are working with basic primitive values like strings, integers, and arrays, and you use PHP 7+ and you can't use polymorphism but you still feel the need to type-check, you should consider type declaration or strict mode. It provides you with static typing on top of standard PHP syntax. The problem with manually type-checking is that doing it will require so much extra verbiage that the faux "type-safety" you get doesn't make up for the lost readability. Keep your PHP clean, write good tests, and have good code reviews. Otherwise, do all of that but with PHP strict type declaration or strict mode.

Bad:

function combine($val1, $val2): int
{
    if (!is_numeric($val1) || !is_numeric($val2)) {
        throw new \Exception('Must be of type Number');
    }

    return $val1 + $val2;
}

Good:

function combine(int $val1, int $val2): int
{
    return $val1 + $val2;
}

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Remove dead code

Dead code is just as bad as duplicate code. There's no reason to keep it in your codebase. If it's not being called, get rid of it! It will still be safe in your version history if you still need it.

Bad:

function oldRequestModule(string $url): void
{
    // ...
}

function newRequestModule(string $url): void
{
    // ...
}

$request = newRequestModule($requestUrl);
inventoryTracker('apples', $request, 'www.inventory-awesome.io');

Good:

function requestModule(string $url): void
{
    // ...
}

$request = requestModule($requestUrl);
inventoryTracker('apples', $request, 'www.inventory-awesome.io');

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Objects and Data Structures

Use object encapsulation

In PHP you can set public, protected and private keywords for methods. Using it, you can control properties modification on an object.

• When you want to do more beyond getting an object property, you don't have to look up and change every accessor in your codebase.
• Makes adding validation simple when doing a set.
• Encapsulates the internal representation.
• Easy to add logging and error handling when getting and setting.
• Inheriting this class, you can override default functionality.
• You can lazy load your object's properties, let's say getting it from a server.

Additionally, this is part of Open/Closed principle.

Bad:

class BankAccount
{
    public $balance = 1000;
}

$bankAccount = new BankAccount();

// Buy shoes...
$bankAccount->balance -= 100;

Good:

class BankAccount
{
    private $balance;

    public function __construct(int $balance = 1000)
    {
      $this->balance = $balance;
    }

    public function withdraw(int $amount): void
    {
        if ($amount > $this->balance) {
            throw new \Exception('Amount greater than available balance.');
        }

        $this->balance -= $amount;
    }

    public function deposit(int $amount): void
    {
        $this->balance += $amount;
    }

    public function getBalance(): int
    {
        return $this->balance;
    }
}

$bankAccount = new BankAccount();

// Buy shoes...
$bankAccount->withdraw($shoesPrice);

// Get balance
$balance = $bankAccount->getBalance();

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Make objects have private/protected members

• public methods and properties are most dangerous for changes, because some outside code may easily rely on them and you can't control what code relies on them. Modifications in class are dangerous for all users of class.
• protected modifier are as dangerous as public, because they are available in scope of any child class. This effectively means that difference between public and protected is only in access mechanism, but encapsulation guarantee remains the same. Modifications in class are dangerous for all descendant classes.
• private modifier guarantees that code is dangerous to modify only in boundaries of single class (you are safe for modifications and you won't have Jenga effect).

Therefore, use private by default and public/protected when you need to provide access for external classes.

For more informations you can read the blog post on this topic written by Fabien Potencier.

Bad:

class Employee
{
    public $name;

    public function __construct(string $name)
    {
        $this->name = $name;
    }
}

$employee = new Employee('John Doe');
echo 'Employee name: '.$employee->name; // Employee name: John Doe

Good:

class Employee
{
    private $name;

    public function __construct(string $name)
    {
        $this->name = $name;
    }

    public function getName(): string
    {
        return $this->name;
    }
}

$employee = new Employee('John Doe');
echo 'Employee name: '.$employee->getName(); // Employee name: John Doe

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Classes

Prefer composition over inheritance

As stated famously in Design Patterns by the Gang of Four, you should prefer composition over inheritance where you can. There are lots of good reasons to use inheritance and lots of good reasons to use composition. The main point for this maxim is that if your mind instinctively goes for inheritance, try to think if composition could model your problem better. In some cases it can.

You might be wondering then, "when should I use inheritance?" It depends on your problem at hand, but this is a decent list of when inheritance makes more sense than composition:

1. Your inheritance represents an "is-a" relationship and not a "has-a" relationship (Human->Animal vs. User->UserDetails).
2. You can reuse code from the base classes (Humans can move like all animals).
3. You want to make global changes to derived classes by changing a base class. (Change the caloric expenditure of all animals when they move).

Bad:

class Employee 
{
    private $name;
    private $email;

    public function __construct(string $name, string $email)
    {
        $this->name = $name;
        $this->email = $email;
    }

    // ...
}

// Bad because Employees "have" tax data. 
// EmployeeTaxData is not a type of Employee

class EmployeeTaxData extends Employee 
{
    private $ssn;
    private $salary;
    
    public function __construct(string $name, string $email, string $ssn, string $salary)
    {
        parent::__construct($name, $email);

        $this->ssn = $ssn;
        $this->salary = $salary;
    }

    // ...
}

Good:

class EmployeeTaxData 
{
    private $ssn;
    private $salary;

    public function __construct(string $ssn, string $salary)
    {
        $this->ssn = $ssn;
        $this->salary = $salary;
    }

    // ...
}

class Employee 
{
    private $name;
    private $email;
    private $taxData;

    public function __construct(string $name, string $email)
    {
        $this->name = $name;
        $this->email = $email;
    }

    public function setTaxData(string $ssn, string $salary)
    {
        $this->taxData = new EmployeeTaxData($ssn, $salary);
    }

    // ...
}

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Avoid fluent interfaces

A Fluent interface is an object oriented API that aims to improve the readability of the source code by using Method chaining.

While there can be some contexts, frequently builder objects, where this pattern reduces the verbosity of the code (for example the PHPUnit Mock Builder or the Doctrine Query Builder), more often it comes at some costs:

1. Breaks Encapsulation.
2. Breaks Decorators.
3. Is harder to mock in a test suite.
4. Makes diffs of commits harder to read.

For more informations you can read the full blog post on this topic written by Marco Pivetta.

Bad:

class Car
{
    private $make = 'Honda';
    private $model = 'Accord';
    private $color = 'white';

    public function setMake(string $make): self
    {
        $this->make = $make;

        // NOTE: Returning this for chaining
        return $this;
    }

    public function setModel(string $model): self
    {
        $this->model = $model;

        // NOTE: Returning this for chaining
        return $this;
    }

    public function setColor(string $color): self
    {
        $this->color = $color;

        // NOTE: Returning this for chaining
        return $this;
    }

    public function dump(): void
    {
        var_dump($this->make, $this->model, $this->color);
    }
}

$car = (new Car())
  ->setColor('pink')
  ->setMake('Ford')
  ->setModel('F-150')
  ->dump();

Good:

class Car
{
    private $make = 'Honda';
    private $model = 'Accord';
    private $color = 'white';

    public function setMake(string $make): void
    {
        $this->make = $make;
    }

    public function setModel(string $model): void
    {
        $this->model = $model;
    }

    public function setColor(string $color): void
    {
        $this->color = $color;
    }

    public function dump(): void
    {
        var_dump($this->make, $this->model, $this->color);
    }
}

$car = new Car();
$car->setColor('pink');
$car->setMake('Ford');
$car->setModel('F-150');
$car->dump();

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Prefer final classes

The final should be used whenever possible:

1. It prevents uncontrolled inheritance chain.
2. It encourages composition.
3. It encourages the Single Responsibility Pattern.
4. It encourages developers to use your public methods instead of extending the class to get access on protected ones.
5. It allows you to change your code without any break of applications that use your class.

The only condition is that your class should implement an interface and no other public methods are defined.

For more informations you can read the blog post on this topic written by Marco Pivetta (Ocramius).

Bad:

final class Car
{
    private $color;
    
    public function __construct($color)
    {
        $this->color = $color;
    }
    
    /**
     * @return string The color of the vehicle
     */
    public function getColor() 
    {
        return $this->color;
    }
}

Good:

interface Vehicle
{
    /**
     * @return string The color of the vehicle
     */
    public function getColor();
}

final class Car implements Vehicle
{
    private $color;
    
    public function __construct($color)
    {
        $this->color = $color;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getColor() 
    {
        return $this->color;
    }
}

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SOLID

SOLID is the mnemonic acronym introduced by Michael Feathers for the first five principles named by Robert Martin, which meant five basic principles of object-oriented programming and design.

• S: Single Responsibility Principle (SRP)
• O: Open/Closed Principle (OCP)
• L: Liskov Substitution Principle (LSP)
• I: Interface Segregation Principle (ISP)
• D: Dependency Inversion Principle (DIP)

Single Responsibility Principle (SRP)

As stated in Clean Code, "There should never be more than one reason for a class to change". It's tempting to jam-pack a class with a lot of functionality, like when you can only take one suitcase on your flight. The issue with this is that your class won't be conceptually cohesive and it will give it many reasons to change. Minimizing the amount of times you need to change a class is important. It's important because if too much functionality is in one class and you modify a piece of it, it can be difficult to understand how that will affect other dependent modules in your codebase.

Bad:

class UserSettings
{
    private $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }

    public function changeSettings(array $settings): void
    {
        if ($this->verifyCredentials()) {
            // ...
        }
    }

    private function verifyCredentials(): bool
    {
        // ...
    }
}

Good:

class UserAuth 
{
    private $user;

    public function __construct(User $user)
    {
        $this->user = $user;
    }
    
    public function verifyCredentials(): bool
    {
        // ...
    }
}

class UserSettings 
{
    private $user;
    private $auth;

    public function __construct(User $user) 
    {
        $this->user = $user;
        $this->auth = new UserAuth($user);
    }

    public function changeSettings(array $settings): void
    {
        if ($this->auth->verifyCredentials()) {
            // ...
        }
    }
}

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Open/Closed Principle (OCP)

As stated by Bertrand Meyer, "software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification." What does that mean though? This principle basically states that you should allow users to add new functionalities without changing existing code.

Bad:

abstract class Adapter
{
    protected $name;

    public function getName(): string
    {
        return $this->name;
    }
}

class AjaxAdapter extends Adapter
{
    public function __construct()
    {
        parent::__construct();

        $this->name = 'ajaxAdapter';
    }
}

class NodeAdapter extends Adapter
{
    public function __construct()
    {
        parent::__construct();

        $this->name = 'nodeAdapter';
    }
}

class HttpRequester
{
    private $adapter;

    public function __construct(Adapter $adapter)
    {
        $this->adapter = $adapter;
    }

    public function fetch(string $url): Promise
    {
        $adapterName = $this->adapter->getName();

        if ($adapterName === 'ajaxAdapter') {
            return $this->makeAjaxCall($url);
        } elseif ($adapterName === 'httpNodeAdapter') {
            return $this->makeHttpCall($url);
        }
    }

    private function makeAjaxCall(string $url): Promise
    {
        // request and return promise
    }

    private function makeHttpCall(string $url): Promise
    {
        // request and return promise
    }
}

Good:

interface Adapter
{
    public function request(string $url): Promise;
}

class AjaxAdapter implements Adapter
{
    public function request(string $url): Promise
    {
        // request and return promise
    }
}

class NodeAdapter implements Adapter
{
    public function request(string $url): Promise
    {
        // request and return promise
    }
}

class HttpRequester
{
    private $adapter;

    public function __construct(Adapter $adapter)
    {
        $this->adapter = $adapter;
    }

    public function fetch(string $url): Promise
    {
        return $this->adapter->request($url);
    }
}

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Liskov Substitution Principle (LSP)

This is a scary term for a very simple concept. It's formally defined as "If S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e., objects of type S may substitute objects of type T) without altering any of the desirable properties of that program (correctness, task performed, etc.)." That's an even scarier definition.

The best explanation for this is if you have a parent class and a child class, then the base class and child class can be used interchangeably without getting incorrect results. This might still be confusing, so let's take a look at the classic Square-Rectangle example. Mathematically, a square is a rectangle, but if you model it using the "is-a" relationship via inheritance, you quickly get into trouble.

Bad:

class Rectangle
{
    protected $width = 0;
    protected $height = 0;

    public function setWidth(int $width): void
    {
        $this->width = $width;
    }

    public function setHeight(int $height): void
    {
        $this->height = $height;
    }

    public function getArea(): int
    {
        return $this->width * $this->height;
    }
}

class Square extends Rectangle
{
    public function setWidth(int $width): void
    {
        $this->width = $this->height = $width;
    }

    public function setHeight(int $height): void
    {
        $this->width = $this->height = $height;
    }
}

function printArea(Rectangle $rectangle): void
{
    $rectangle->setWidth(4);
    $rectangle->setHeight(5);
 
    // BAD: Will return 25 for Square. Should be 20.
    echo sprintf('%s has area %d.', get_class($rectangle), $rectangle->getArea()).PHP_EOL;
}

$rectangles = [new Rectangle(), new Square()];

foreach ($rectangles as $rectangle) {
    printArea($rectangle);
}

Good:

The best way is separate the quadrangles and allocation of a more general subtype for both shapes.

Despite the apparent similarity of the square and the rectangle, they are different. A square has much in common with a rhombus, and a rectangle with a parallelogram, but they are not subtype. A square, a rectangle, a rhombus and a parallelogram are separate shapes with their own properties, albeit similar.

interface Shape
{
    public function getArea(): int;
}

class Rectangle implements Shape
{
    private $width = 0;
    private $height = 0;

    public function __construct(int $width, int $height)
    {
        $this->width = $width;
        $this->height = $height;
    }

    public function getArea(): int
    {
        return $this->width * $this->height;
    }
}

class Square implements Shape
{
    private $length = 0;

    public function __construct(int $length)
    {
        $this->length = $length;
    }

    public function getArea(): int
    {
        return $this->length ** 2;
    }
}

function printArea(Shape $shape): void
{
    echo sprintf('%s has area %d.', get_class($shape), $shape->getArea()).PHP_EOL;
}

$shapes = [new Rectangle(4, 5), new Square(5)];

foreach ($shapes as $shape) {
    printArea($shape);
}

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Interface Segregation Principle (ISP)

ISP states that "Clients should not be forced to depend upon interfaces that they do not use."

A good example to look at that demonstrates this principle is for classes that require large settings objects. Not requiring clients to set up huge amounts of options is beneficial, because most of the time they won't need all of the settings. Making them optional helps prevent having a "fat interface".

Bad:

interface Employee
{
    public function work(): void;

    public function eat(): void;
}

class Human implements Employee
{
    public function work(): void
    {
        // ....working
    }

    public function eat(): void
    {
        // ...... eating in lunch break
    }
}

class Robot implements Employee
{
    public function work(): void
    {
        //.... working much more
    }

    public function eat(): void
    {
        //.... robot can't eat, but it must implement this method
    }
}

Good:

Not every worker is an employee, but every employee is a worker.

interface Workable
{
    public function work(): void;
}

interface Feedable
{
    public function eat(): void;
}

interface Employee extends Feedable, Workable
{
}

class Human implements Employee
{
    public function work(): void
    {
        // ....working
    }

    public function eat(): void
    {
        //.... eating in lunch break
    }
}

// robot can only work
class Robot implements Workable
{
    public function work(): void
    {
        // ....working
    }
}

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Dependency Inversion Principle (DIP)

This principle states two essential things:

1. High-level modules should not depend on low-level modules. Both should depend on abstractions.
2. Abstractions should not depend upon details. Details should depend on abstractions.

This can be hard to understand at first, but if you've worked with PHP frameworks (like Symfony), you've seen an implementation of this principle in the form of Dependency Injection (DI). While they are not identical concepts, DIP keeps high-level modules from knowing the details of its low-level modules and setting them up. It can accomplish this through DI. A huge benefit of this is that it reduces the coupling between modules. Coupling is a very bad development pattern because it makes your code hard to refactor.

Bad:

class Employee
{
    public function work(): void
    {
        // ....working
    }
}

class Robot extends Employee
{
    public function work(): void
    {
        //.... working much more
    }
}

class Manager
{
    private $employee;

    public function __construct(Employee $employee)
    {
        $this->employee = $employee;
    }

    public function manage(): void
    {
        $this->employee->work();
    }
}

Good:

interface Employee
{
    public function work(): void;
}

class Human implements Employee
{
    public function work(): void
    {
        // ....working
    }
}

class Robot implements Employee
{
    public function work(): void
    {
        //.... working much more
    }
}

class Manager
{
    private $employee;

    public function __construct(Employee $employee)
    {
        $this->employee = $employee;
    }

    public function manage(): void
    {
        $this->employee->work();
    }
}

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Don’t repeat yourself (DRY)

Try to observe the DRY principle.

Do your absolute best to avoid duplicate code. Duplicate code is bad because it means that there's more than one place to alter something if you need to change some logic.

Imagine if you run a restaurant and you keep track of your inventory: all your tomatoes, onions, garlic, spices, etc. If you have multiple lists that you keep this on, then all have to be updated when you serve a dish with tomatoes in them. If you only have one list, there's only one place to update!

Often you have duplicate code because you have two or more slightly different things, that share a lot in common, but their differences force you to have two or more separate functions that do much of the same things. Removing duplicate code means creating an abstraction that can handle this set of different things with just one function/module/class.

Getting the abstraction right is critical, that's why you should follow the SOLID principles laid out in the Classes section. Bad abstractions can be worse than duplicate code, so be careful! Having said this, if you can make a good abstraction, do it! Don't repeat yourself, otherwise you'll find yourself updating multiple places any time you want to change one thing.

Bad:

function showDeveloperList(array $developers): void
{
    foreach ($developers as $developer) {
        $expectedSalary = $developer->calculateExpectedSalary();
        $experience = $developer->getExperience();
        $githubLink = $developer->getGithubLink();
        $data = [
            $expectedSalary,
            $experience,
            $githubLink
        ];

        render($data);
    }
}

function showManagerList(array $managers): void
{
    foreach ($managers as $manager) {
        $expectedSalary = $manager->calculateExpectedSalary();
        $experience = $manager->getExperience();
        $githubLink = $manager->getGithubLink();
        $data = [
            $expectedSalary,
            $experience,
            $githubLink
        ];

        render($data);
    }
}

Good:

function showList(array $employees): void
{
    foreach ($employees as $employee) {
        $expectedSalary = $employee->calculateExpectedSalary();
        $experience = $employee->getExperience();
        $githubLink = $employee->getGithubLink();
        $data = [
            $expectedSalary,
            $experience,
            $githubLink
        ];

        render($data);
    }
}

Very good:

It is better to use a compact version of the code.

function showList(array $employees): void
{
    foreach ($employees as $employee) {
        render([
            $employee->calculateExpectedSalary(),
            $employee->getExperience(),
            $employee->getGithubLink()
        ]);
    }
}

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Translations

This is also available in other languages:

• 🇨🇳 Chinese:
  • php-cpm/clean-code-php
• 🇷🇺 Russian:
  • peter-gribanov/clean-code-php
• 🇪🇸 Spanish:
  • fikoborquez/clean-code-php
• 🇧🇷 Portuguese:
  • fabioars/clean-code-php
  • jeanjar/clean-code-php
• 🇹🇭 Thai:
  • panuwizzle/clean-code-php
• 🇫🇷 French:
  • errorname/clean-code-php
• 🇻🇳 Vietnamese
  • viethuongdev/clean-code-php
• 🇰🇷 Korean:
  • yujineeee/clean-code-php

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