Auto merge of #294 - nical:try-cst, r=kvark

Make cast infallible and add try_cast.

Fixes #270.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/euclid/294)
<!-- Reviewable:end -->

src/length.rs

@@ -211,7 +211,12 @@ impl<U, T: Clone + Neg<Output = T>> Neg for Length<T, U> {
 
 impl<Unit, T0: NumCast + Clone> Length<T0, Unit> {
     /// Cast from one numeric representation to another, preserving the units.
-    pub fn cast<T1: NumCast + Clone>(&self) -> Option<Length<T1, Unit>> {
+    pub fn cast<T1: NumCast + Clone>(&self) -> Length<T1, Unit> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    pub fn try_cast<T1: NumCast + Clone>(&self) -> Option<Length<T1, Unit>> {
         NumCast::from(self.get()).map(Length::new)
     }
 }
@@ -461,7 +466,7 @@ mod tests {
     fn test_cast() {
         let length_as_i32: Length<i32, Cm> = Length::new(5);
 
-        let result: Length<f32, Cm> = length_as_i32.cast().unwrap();
+        let result: Length<f32, Cm> = length_as_i32.cast();
 
         let length_as_f32: Length<f32, Cm> = Length::new(5.0);
         assert_eq!(result, length_as_f32);

src/point.rs

@@ -286,7 +286,16 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// as one would expect from a simple cast, but this behavior does not always make sense
     /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
     #[inline]
-    pub fn cast<NewT: NumCast + Copy>(&self) -> Option<TypedPoint2D<NewT, U>> {
+    pub fn cast<NewT: NumCast + Copy>(&self) -> TypedPoint2D<NewT, U> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    ///
+    /// When casting from floating point to integer coordinates, the decimals are truncated
+    /// as one would expect from a simple cast, but this behavior does not always make sense
+    /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
+    pub fn try_cast<NewT: NumCast + Copy>(&self) -> Option<TypedPoint2D<NewT, U>> {
         match (NumCast::from(self.x), NumCast::from(self.y)) {
             (Some(x), Some(y)) => Some(point2(x, y)),
             _ => None,
@@ -298,13 +307,13 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// Cast into an `f32` point.
     #[inline]
     pub fn to_f32(&self) -> TypedPoint2D<f32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `f64` point.
     #[inline]
     pub fn to_f64(&self) -> TypedPoint2D<f64, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `usize` point, truncating decimals if any.
@@ -314,7 +323,7 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_usize(&self) -> TypedPoint2D<usize, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `u32` point, truncating decimals if any.
@@ -324,7 +333,7 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_u32(&self) -> TypedPoint2D<u32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an i32 point, truncating decimals if any.
@@ -334,7 +343,7 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_i32(&self) -> TypedPoint2D<i32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an i64 point, truncating decimals if any.
@@ -344,7 +353,7 @@ impl<T: NumCast + Copy, U> TypedPoint2D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_i64(&self) -> TypedPoint2D<i64, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 }
 
@@ -650,7 +659,17 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// as one would expect from a simple cast, but this behavior does not always make sense
     /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
     #[inline]
-    pub fn cast<NewT: NumCast + Copy>(&self) -> Option<TypedPoint3D<NewT, U>> {
+    pub fn cast<NewT: NumCast + Copy>(&self) -> TypedPoint3D<NewT, U> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    ///
+    /// When casting from floating point to integer coordinates, the decimals are truncated
+    /// as one would expect from a simple cast, but this behavior does not always make sense
+    /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
+    #[inline]
+    pub fn try_cast<NewT: NumCast + Copy>(&self) -> Option<TypedPoint3D<NewT, U>> {
         match (
             NumCast::from(self.x),
             NumCast::from(self.y),
@@ -666,13 +685,13 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// Cast into an `f32` point.
     #[inline]
     pub fn to_f32(&self) -> TypedPoint3D<f32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `f64` point.
     #[inline]
     pub fn to_f64(&self) -> TypedPoint3D<f64, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `usize` point, truncating decimals if any.
@@ -682,7 +701,7 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_usize(&self) -> TypedPoint3D<usize, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `u32` point, truncating decimals if any.
@@ -692,7 +711,7 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_u32(&self) -> TypedPoint3D<u32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i32` point, truncating decimals if any.
@@ -702,7 +721,7 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_i32(&self) -> TypedPoint3D<i32, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i64` point, truncating decimals if any.
@@ -712,7 +731,7 @@ impl<T: NumCast + Copy, U> TypedPoint3D<T, U> {
     /// the desired conversion behavior.
     #[inline]
     pub fn to_i64(&self) -> TypedPoint3D<i64, U> {
-        self.cast().unwrap()
+        self.cast()
     }
 }
 

src/rect.rs

@@ -470,8 +470,20 @@ impl<T0: NumCast + Copy, Unit> TypedRect<T0, Unit> {
     /// When casting from floating point to integer coordinates, the decimals are truncated
     /// as one would expect from a simple cast, but this behavior does not always make sense
     /// geometrically. Consider using round(), round_in or round_out() before casting.
-    pub fn cast<T1: NumCast + Copy>(&self) -> Option<TypedRect<T1, Unit>> {
-        match (self.origin.cast(), self.size.cast()) {
+    pub fn cast<T1: NumCast + Copy>(&self) -> TypedRect<T1, Unit> {
+        TypedRect::new(
+            self.origin.cast(),
+            self.size.cast(),
+        )
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    ///
+    /// When casting from floating point to integer coordinates, the decimals are truncated
+    /// as one would expect from a simple cast, but this behavior does not always make sense
+    /// geometrically. Consider using round(), round_in or round_out() before casting.
+    pub fn try_cast<T1: NumCast + Copy>(&self) -> Option<TypedRect<T1, Unit>> {
+        match (self.origin.try_cast(), self.size.try_cast()) {
             (Some(origin), Some(size)) => Some(TypedRect::new(origin, size)),
             _ => None,
         }
@@ -518,12 +530,12 @@ impl<T: Floor + Ceil + Round + Add<T, Output = T> + Sub<T, Output = T>, U> Typed
 impl<T: NumCast + Copy, Unit> TypedRect<T, Unit> {
     /// Cast into an `f32` rectangle.
     pub fn to_f32(&self) -> TypedRect<f32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `f64` rectangle.
     pub fn to_f64(&self) -> TypedRect<f64, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `usize` rectangle, truncating decimals if any.
@@ -532,7 +544,7 @@ impl<T: NumCast + Copy, Unit> TypedRect<T, Unit> {
     /// to `round()`, `round_in()` or `round_out()` before the cast in order to
     /// obtain the desired conversion behavior.
     pub fn to_usize(&self) -> TypedRect<usize, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `u32` rectangle, truncating decimals if any.
@@ -541,7 +553,7 @@ impl<T: NumCast + Copy, Unit> TypedRect<T, Unit> {
     /// to `round()`, `round_in()` or `round_out()` before the cast in order to
     /// obtain the desired conversion behavior.
     pub fn to_u32(&self) -> TypedRect<u32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i32` rectangle, truncating decimals if any.
@@ -550,7 +562,7 @@ impl<T: NumCast + Copy, Unit> TypedRect<T, Unit> {
     /// to `round()`, `round_in()` or `round_out()` before the cast in order to
     /// obtain the desired conversion behavior.
     pub fn to_i32(&self) -> TypedRect<i32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i64` rectangle, truncating decimals if any.
@@ -559,7 +571,7 @@ impl<T: NumCast + Copy, Unit> TypedRect<T, Unit> {
     /// to `round()`, `round_in()` or `round_out()` before the cast in order to
     /// obtain the desired conversion behavior.
     pub fn to_i64(&self) -> TypedRect<i64, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 }
 

src/scale.rs

@@ -123,7 +123,12 @@ impl<T: Clone + Sub<T, Output = T>, Src, Dst> Sub for TypedScale<T, Src, Dst> {
 
 impl<T: NumCast + Clone, Src, Dst0> TypedScale<T, Src, Dst0> {
     /// Cast from one numeric representation to another, preserving the units.
-    pub fn cast<T1: NumCast + Clone>(&self) -> Option<TypedScale<T1, Src, Dst0>> {
+    pub fn cast<T1: NumCast + Clone>(&self) -> TypedScale<T1, Src, Dst0> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    pub fn try_cast<T1: NumCast + Clone>(&self) -> Option<TypedScale<T1, Src, Dst0>> {
         NumCast::from(self.get()).map(TypedScale::new)
     }
 }

src/size.rs

@@ -216,7 +216,16 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
     /// When casting from floating point to integer coordinates, the decimals are truncated
     /// as one would expect from a simple cast, but this behavior does not always make sense
     /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
-    pub fn cast<NewT: NumCast + Copy>(&self) -> Option<TypedSize2D<NewT, Unit>> {
+    pub fn cast<NewT: NumCast + Copy>(&self) -> TypedSize2D<NewT, Unit> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    ///
+    /// When casting from floating point to integer coordinates, the decimals are truncated
+    /// as one would expect from a simple cast, but this behavior does not always make sense
+    /// geometrically. Consider using `round()`, `ceil()` or `floor()` before casting.
+    pub fn try_cast<NewT: NumCast + Copy>(&self) -> Option<TypedSize2D<NewT, Unit>> {
         match (NumCast::from(self.width), NumCast::from(self.height)) {
             (Some(w), Some(h)) => Some(TypedSize2D::new(w, h)),
             _ => None,
@@ -227,12 +236,12 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
 
     /// Cast into an `f32` size.
     pub fn to_f32(&self) -> TypedSize2D<f32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `f64` size.
     pub fn to_f64(&self) -> TypedSize2D<f64, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `uint` size, truncating decimals if any.
@@ -241,7 +250,7 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
     /// to `round()`, `ceil()` or `floor()` before the cast in order to obtain
     /// the desired conversion behavior.
     pub fn to_usize(&self) -> TypedSize2D<usize, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `u32` size, truncating decimals if any.
@@ -250,7 +259,7 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
     /// to `round()`, `ceil()` or `floor()` before the cast in order to obtain
     /// the desired conversion behavior.
     pub fn to_u32(&self) -> TypedSize2D<u32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i32` size, truncating decimals if any.
@@ -259,7 +268,7 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
     /// to `round()`, `ceil()` or `floor()` before the cast in order to obtain
     /// the desired conversion behavior.
     pub fn to_i32(&self) -> TypedSize2D<i32, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 
     /// Cast into an `i64` size, truncating decimals if any.
@@ -268,7 +277,7 @@ impl<T: NumCast + Copy, Unit> TypedSize2D<T, Unit> {
     /// to `round()`, `ceil()` or `floor()` before the cast in order to obtain
     /// the desired conversion behavior.
     pub fn to_i64(&self) -> TypedSize2D<i64, Unit> {
-        self.cast().unwrap()
+        self.cast()
     }
 }
 

src/transform2d.rs

@@ -134,16 +134,23 @@ impl<T: Copy, Src, Dst> TypedTransform2D<T, Src, Dst> {
 
 impl<T0: NumCast + Copy, Src, Dst> TypedTransform2D<T0, Src, Dst> {
     /// Cast from one numeric representation to another, preserving the units.
-    pub fn cast<T1: NumCast + Copy>(&self) -> Option<TypedTransform2D<T1, Src, Dst>> {
+    pub fn cast<T1: NumCast + Copy>(&self) -> TypedTransform2D<T1, Src, Dst> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    pub fn try_cast<T1: NumCast + Copy>(&self) -> Option<TypedTransform2D<T1, Src, Dst>> {
         match (NumCast::from(self.m11), NumCast::from(self.m12),
                NumCast::from(self.m21), NumCast::from(self.m22),
                NumCast::from(self.m31), NumCast::from(self.m32)) {
             (Some(m11), Some(m12),
              Some(m21), Some(m22),
              Some(m31), Some(m32)) => {
-                Some(TypedTransform2D::row_major(m11, m12,
-                                                 m21, m22,
-                                                 m31, m32))
+                Some(TypedTransform2D::row_major(
+                    m11, m12,
+                    m21, m22,
+                    m31, m32
+                ))
             },
             _ => None
         }

src/transform3d.rs

@@ -692,7 +692,12 @@ impl<T: Copy, Src, Dst> TypedTransform3D<T, Src, Dst> {
 
 impl<T0: NumCast + Copy, Src, Dst> TypedTransform3D<T0, Src, Dst> {
     /// Cast from one numeric representation to another, preserving the units.
-    pub fn cast<T1: NumCast + Copy>(&self) -> Option<TypedTransform3D<T1, Src, Dst>> {
+    pub fn cast<T1: NumCast + Copy>(&self) -> TypedTransform3D<T1, Src, Dst> {
+        self.try_cast().unwrap()
+    }
+
+    /// Fallible cast from one numeric representation to another, preserving the units.
+    pub fn try_cast<T1: NumCast + Copy>(&self) -> Option<TypedTransform3D<T1, Src, Dst>> {
         match (NumCast::from(self.m11), NumCast::from(self.m12),
                NumCast::from(self.m13), NumCast::from(self.m14),
                NumCast::from(self.m21), NumCast::from(self.m22),