Add reason for each 'must_use'

2 files changed, 58 insertions, 58 deletions

diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs
index d0c64243ee3..3c08b254466 100644
--- a/src/libstd/f32.rs
+++ b/src/libstd/f32.rs
@@ -40,7 +40,7 @@ impl f32 {
     /// assert_eq!(g.floor(), 3.0);
     /// assert_eq!(h.floor(), -4.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn floor(self) -> f32 {
@@ -74,7 +74,7 @@ impl f32 {
     /// assert_eq!(f.ceil(), 4.0);
     /// assert_eq!(g.ceil(), 4.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ceil(self) -> f32 {
@@ -97,7 +97,7 @@ impl f32 {
     /// assert_eq!(f.round(), 3.0);
     /// assert_eq!(g.round(), -3.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn round(self) -> f32 {
@@ -117,7 +117,7 @@ impl f32 {
     /// assert_eq!(g.trunc(), 3.0);
     /// assert_eq!(h.trunc(), -3.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn trunc(self) -> f32 {
@@ -139,7 +139,7 @@ impl f32 {
     /// assert!(abs_difference_x <= f32::EPSILON);
     /// assert!(abs_difference_y <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn fract(self) -> f32 { self - self.trunc() }
@@ -163,7 +163,7 @@ impl f32 {
     ///
     /// assert!(f32::NAN.abs().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn abs(self) -> f32 {
@@ -188,7 +188,7 @@ impl f32 {
     ///
     /// assert!(f32::NAN.signum().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn signum(self) -> f32 {
@@ -221,7 +221,7 @@ impl f32 {
     /// assert!(f32::NAN.copysign(1.0).is_nan());
     /// ```
     #[inline]
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "copysign", since = "1.35.0")]
     pub fn copysign(self, sign: f32) -> f32 {
         unsafe { intrinsics::copysignf32(self, sign) }
@@ -374,7 +374,7 @@ impl f32 {
     /// assert!(abs_difference <= f32::EPSILON);
     /// assert!(negative.sqrt().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sqrt(self) -> f32 {
@@ -401,7 +401,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp(self) -> f32 {
@@ -426,7 +426,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp2(self) -> f32 {
@@ -449,7 +449,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln(self) -> f32 {
@@ -496,7 +496,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log2(self) -> f32 {
@@ -520,7 +520,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log10(self) -> f32 {
@@ -578,7 +578,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cbrt(self) -> f32 {
@@ -620,7 +620,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sin(self) -> f32 {
@@ -644,7 +644,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cos(self) -> f32 {
@@ -667,7 +667,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tan(self) -> f32 {
@@ -690,7 +690,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asin(self) -> f32 {
@@ -713,7 +713,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acos(self) -> f32 {
@@ -735,7 +735,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atan(self) -> f32 {
@@ -814,7 +814,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp_m1(self) -> f32 {
@@ -836,7 +836,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln_1p(self) -> f32 {
@@ -860,7 +860,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sinh(self) -> f32 {
@@ -884,7 +884,7 @@ impl f32 {
     /// // Same result
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cosh(self) -> f32 {
@@ -908,7 +908,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tanh(self) -> f32 {
@@ -929,7 +929,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f32 {
@@ -954,7 +954,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= f32::EPSILON);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acosh(self) -> f32 {
@@ -978,7 +978,7 @@ impl f32 {
     ///
     /// assert!(abs_difference <= 1e-5);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atanh(self) -> f32 {
diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs
index 0878cfd68b4..74c81b47bbb 100644
--- a/src/libstd/f64.rs
+++ b/src/libstd/f64.rs
@@ -40,7 +40,7 @@ impl f64 {
     /// assert_eq!(g.floor(), 3.0);
     /// assert_eq!(h.floor(), -4.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn floor(self) -> f64 {
@@ -58,7 +58,7 @@ impl f64 {
     /// assert_eq!(f.ceil(), 4.0);
     /// assert_eq!(g.ceil(), 4.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ceil(self) -> f64 {
@@ -77,7 +77,7 @@ impl f64 {
     /// assert_eq!(f.round(), 3.0);
     /// assert_eq!(g.round(), -3.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn round(self) -> f64 {
@@ -97,7 +97,7 @@ impl f64 {
     /// assert_eq!(g.trunc(), 3.0);
     /// assert_eq!(h.trunc(), -3.0);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn trunc(self) -> f64 {
@@ -117,7 +117,7 @@ impl f64 {
     /// assert!(abs_difference_x < 1e-10);
     /// assert!(abs_difference_y < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn fract(self) -> f64 { self - self.trunc() }
@@ -141,7 +141,7 @@ impl f64 {
     ///
     /// assert!(f64::NAN.abs().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn abs(self) -> f64 {
@@ -166,7 +166,7 @@ impl f64 {
     ///
     /// assert!(f64::NAN.signum().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn signum(self) -> f64 {
@@ -199,7 +199,7 @@ impl f64 {
     /// assert!(f64::NAN.copysign(1.0).is_nan());
     /// ```
     #[inline]
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "copysign", since = "1.35.0")]
     pub fn copysign(self, sign: f64) -> f64 {
         unsafe { intrinsics::copysignf64(self, sign) }
@@ -339,7 +339,7 @@ impl f64 {
     /// assert!(abs_difference < 1e-10);
     /// assert!(negative.sqrt().is_nan());
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sqrt(self) -> f64 {
@@ -364,7 +364,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp(self) -> f64 {
@@ -383,7 +383,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp2(self) -> f64 {
@@ -404,7 +404,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln(self) -> f64 {
@@ -443,7 +443,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log2(self) -> f64 {
@@ -467,7 +467,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn log10(self) -> f64 {
@@ -517,7 +517,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cbrt(self) -> f64 {
@@ -557,7 +557,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sin(self) -> f64 {
@@ -577,7 +577,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cos(self) -> f64 {
@@ -596,7 +596,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-14);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tan(self) -> f64 {
@@ -619,7 +619,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asin(self) -> f64 {
@@ -642,7 +642,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acos(self) -> f64 {
@@ -662,7 +662,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atan(self) -> f64 {
@@ -739,7 +739,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn exp_m1(self) -> f64 {
@@ -761,7 +761,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn ln_1p(self) -> f64 {
@@ -785,7 +785,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn sinh(self) -> f64 {
@@ -809,7 +809,7 @@ impl f64 {
     /// // Same result
     /// assert!(abs_difference < 1.0e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn cosh(self) -> f64 {
@@ -833,7 +833,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn tanh(self) -> f64 {
@@ -852,7 +852,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn asinh(self) -> f64 {
@@ -875,7 +875,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn acosh(self) -> f64 {
@@ -899,7 +899,7 @@ impl f64 {
     ///
     /// assert!(abs_difference < 1.0e-10);
     /// ```
-    #[must_use]
+    #[must_use = "method returns a new number and does not mutate the original value"]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn atanh(self) -> f64 {