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Add #[must_use] message to Fn* traits #58262

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Feb 11, 2019
Merged

Add #[must_use] message to Fn* traits #58262

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6 changes: 3 additions & 3 deletions src/libcore/ops/function.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,7 @@
label="expected an `Fn<{Args}>` closure, found `{Self}`",
)]
#[fundamental] // so that regex can rely that `&str: !FnMut`
#[must_use]
#[must_use = "closures are lazy and do nothing unless called"]
pub trait Fn<Args> : FnMut<Args> {
/// Performs the call operation.
#[unstable(feature = "fn_traits", issue = "29625")]
Expand Down Expand Up @@ -141,7 +141,7 @@ pub trait Fn<Args> : FnMut<Args> {
label="expected an `FnMut<{Args}>` closure, found `{Self}`",
)]
#[fundamental] // so that regex can rely that `&str: !FnMut`
#[must_use]
#[must_use = "closures are lazy and do nothing unless called"]
pub trait FnMut<Args> : FnOnce<Args> {
/// Performs the call operation.
#[unstable(feature = "fn_traits", issue = "29625")]
Expand Down Expand Up @@ -220,7 +220,7 @@ pub trait FnMut<Args> : FnOnce<Args> {
label="expected an `FnOnce<{Args}>` closure, found `{Self}`",
)]
#[fundamental] // so that regex can rely that `&str: !FnMut`
#[must_use]
#[must_use = "closures are lazy and do nothing unless called"]
pub trait FnOnce<Args> {
/// The returned type after the call operator is used.
#[stable(feature = "fn_once_output", since = "1.12.0")]
Expand Down