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Add missing examples on core traits' method #76568

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Sep 10, 2020
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Add missing examples on core traits' method #76568

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77 changes: 77 additions & 0 deletions library/core/src/ops/arith.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,12 @@ pub trait Add<Rhs = Self> {
type Output;

/// Performs the `+` operation.
///
/// # Example
///
/// ```
/// assert_eq!(12 + 1, 13);
/// ```
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@pickfire pickfire Sep 10, 2020 •
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Should we mention somewhere what happens when add overflow on debug build and release build? IIRC it behaves differently.

#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn add(self, rhs: Rhs) -> Self::Output;
Expand Down Expand Up @@ -178,6 +184,12 @@ pub trait Sub<Rhs = Self> {
type Output;

/// Performs the `-` operation.
///
/// # Example
///
/// ```
/// assert_eq!(12 - 1, 11);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn sub(self, rhs: Rhs) -> Self::Output;
Expand Down Expand Up @@ -300,6 +312,12 @@ pub trait Mul<Rhs = Self> {
type Output;

/// Performs the `*` operation.
///
/// # Example
///
/// ```
/// assert_eq!(12 * 2, 24);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn mul(self, rhs: Rhs) -> Self::Output;
Expand Down Expand Up @@ -426,6 +444,12 @@ pub trait Div<Rhs = Self> {
type Output;

/// Performs the `/` operation.
///
/// # Example
///
/// ```
/// assert_eq!(12 / 2, 6);
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How about 12 / 0?

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?? 12/0 is a compile time error: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=750633198d7a3b2f68deffac99eed104

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Exactly, I think it would be good to have another example to show that it will fail to compile.

/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn div(self, rhs: Rhs) -> Self::Output;
Expand Down Expand Up @@ -513,6 +537,12 @@ pub trait Rem<Rhs = Self> {
type Output;

/// Performs the `%` operation.
///
/// # Example
///
/// ```
/// assert_eq!(12 % 10, 2);
/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn rem(self, rhs: Rhs) -> Self::Output;
Expand Down Expand Up @@ -612,6 +642,13 @@ pub trait Neg {
type Output;

/// Performs the unary `-` operation.
///
/// # Example
///
/// ```
/// let x: i32 = 12;
/// assert_eq!(-x, -12);
Comment on lines +649 to +650
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I was going to say something about assert_eq!(-12, -12) and then I realized that was silly lol. So this is fine.

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:D

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How about assert_eq!(0, -0)?

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These suggestions are about the meaning of the operations, you're showing off the edge cases. I don't think this is a good place to document edge cases, this is just showing which operations the trait corresponds to.

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In particular, all these suggestions only make sense for numbers and would be completely out of place if it used Duration or something instead.

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Well, edge cases are considered part of the meanings too, of course users wouldn't want surprises. Or maybe do you have a better idea where to put these edge cases?

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I'd document them on the implementations, not the traits themselves. Take a look at library/core/src/num, maybe. But they certainly don't belong here - this is for every type that implements the trait, not just numbers.

/// ```
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
fn neg(self) -> Self::Output;
Expand Down Expand Up @@ -673,6 +710,14 @@ neg_impl! { isize i8 i16 i32 i64 i128 f32 f64 }
#[doc(alias = "+=")]
pub trait AddAssign<Rhs = Self> {
/// Performs the `+=` operation.
///
/// # Example
///
/// ```
/// let mut x: u32 = 12;
/// x += 1;
/// assert_eq!(x, 13);
/// ```
#[stable(feature = "op_assign_traits", since = "1.8.0")]
fn add_assign(&mut self, rhs: Rhs);
}
Expand Down Expand Up @@ -731,6 +776,14 @@ add_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
#[doc(alias = "-=")]
pub trait SubAssign<Rhs = Self> {
/// Performs the `-=` operation.
///
/// # Example
///
/// ```
/// let mut x: u32 = 12;
/// x -= 1;
/// assert_eq!(x, 11);
/// ```
#[stable(feature = "op_assign_traits", since = "1.8.0")]
fn sub_assign(&mut self, rhs: Rhs);
}
Expand Down Expand Up @@ -780,6 +833,14 @@ sub_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
#[doc(alias = "*=")]
pub trait MulAssign<Rhs = Self> {
/// Performs the `*=` operation.
///
/// # Example
///
/// ```
/// let mut x: u32 = 12;
/// x *= 2;
/// assert_eq!(x, 24);
/// ```
#[stable(feature = "op_assign_traits", since = "1.8.0")]
fn mul_assign(&mut self, rhs: Rhs);
}
Expand Down Expand Up @@ -829,6 +890,14 @@ mul_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
#[doc(alias = "/=")]
pub trait DivAssign<Rhs = Self> {
/// Performs the `/=` operation.
///
/// # Example
///
/// ```
/// let mut x: u32 = 12;
/// x /= 2;
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How about / 0?

/// assert_eq!(x, 6);
/// ```
#[stable(feature = "op_assign_traits", since = "1.8.0")]
fn div_assign(&mut self, rhs: Rhs);
}
Expand Down Expand Up @@ -881,6 +950,14 @@ div_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
#[doc(alias = "%=")]
pub trait RemAssign<Rhs = Self> {
/// Performs the `%=` operation.
///
/// # Example
///
/// ```
/// let mut x: u32 = 12;
/// x %= 10;
/// assert_eq!(x, 2);
/// ```
#[stable(feature = "op_assign_traits", since = "1.8.0")]
fn rem_assign(&mut self, rhs: Rhs);
}
Expand Down