77 lines
1.7 KiB
Rust
77 lines
1.7 KiB
Rust
// build-pass (FIXME(62277): could be check-pass?)
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#![warn(unused_must_use)]
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#[derive(PartialEq, Eq)]
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struct MyStruct {
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n: usize,
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}
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impl MyStruct {
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#[must_use]
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fn need_to_use_this_method_value(&self) -> usize {
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self.n
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}
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#[must_use]
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fn need_to_use_this_associated_function_value() -> isize {
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-1
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}
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}
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trait EvenNature {
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#[must_use = "no side effects"]
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fn is_even(&self) -> bool;
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}
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impl EvenNature for MyStruct {
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fn is_even(&self) -> bool {
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self.n % 2 == 0
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}
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}
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trait Replaceable {
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fn replace(&mut self, substitute: usize) -> usize;
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}
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impl Replaceable for MyStruct {
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// ↓ N.b.: `#[must_use]` attribute on a particular trait implementation
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// method won't work; the attribute should be on the method signature in
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// the trait's definition.
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#[must_use]
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fn replace(&mut self, substitute: usize) -> usize {
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let previously = self.n;
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self.n = substitute;
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previously
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}
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}
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#[must_use = "it's important"]
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fn need_to_use_this_value() -> bool {
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false
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}
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fn main() {
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need_to_use_this_value(); //~ WARN unused return value
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let mut m = MyStruct { n: 2 };
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let n = MyStruct { n: 3 };
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m.need_to_use_this_method_value(); //~ WARN unused return value
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m.is_even(); // trait method!
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//~^ WARN unused return value
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MyStruct::need_to_use_this_associated_function_value();
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//~^ WARN unused return value
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m.replace(3); // won't warn (annotation needs to be in trait definition)
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// comparison methods are `must_use`
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2.eq(&3); //~ WARN unused return value
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m.eq(&n); //~ WARN unused return value
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// lint includes comparison operators
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2 == 3; //~ WARN unused comparison
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m == n; //~ WARN unused comparison
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}
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