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I encountered an instance where an `FnPtr` implemented a trait, but I was passing an `FnDef`. To the end user, there is really no way to differentiate each of them, but it is necessary to cast to the generic function in order to compile. It is thus useful to suggest `as` in the help note, (even if the Fn output implements the trait).
44 lines
1.7 KiB
Plaintext
44 lines
1.7 KiB
Plaintext
error[E0277]: the trait bound `fn() -> bool {example}: Foo` is not satisfied
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--> $DIR/fn-trait-cast-diagnostic.rs:21:15
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LL | do_on_foo(example);
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| --------- ^^^^^^^ the trait `Foo` is not implemented for fn item `fn() -> bool {example}`
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| |
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| required by a bound introduced by this call
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note: required by a bound in `do_on_foo`
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--> $DIR/fn-trait-cast-diagnostic.rs:17:22
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LL | fn do_on_foo(v: impl Foo) {}
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| ^^^ required by this bound in `do_on_foo`
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help: use parentheses to call this function
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LL | do_on_foo(example());
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| ++
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help: the trait `Foo` is implemented for fn pointer `fn() -> bool`, try casting using `as`
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LL | do_on_foo(example as fn() -> bool);
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| +++++++++++++++
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error[E0277]: the trait bound `fn() -> bool {example}: NoOtherFoo` is not satisfied
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--> $DIR/fn-trait-cast-diagnostic.rs:24:22
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LL | do_on_single_foo(example);
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| ---------------- ^^^^^^^ the trait `NoOtherFoo` is not implemented for fn item `fn() -> bool {example}`
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| |
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| required by a bound introduced by this call
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note: required by a bound in `do_on_single_foo`
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--> $DIR/fn-trait-cast-diagnostic.rs:18:29
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LL | fn do_on_single_foo(v: impl NoOtherFoo) {}
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| ^^^^^^^^^^ required by this bound in `do_on_single_foo`
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help: the trait `NoOtherFoo` is implemented for fn pointer `fn() -> bool`, try casting using `as`
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LL | do_on_single_foo(example as fn() -> bool);
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| +++++++++++++++
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0277`.
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