E0281 - Error codes index
Description: Book listing all Rust error codes

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# Error code E0281

#### Note: this error code is no longer emitted by the compiler.

You tried to supply a type which doesn't implement some trait in a location which expected that trait. This error typically occurs when working with `Fn`-based types. Erroneous code example:

    fn foo<F: Fn(usize)>(x: F) { }

    fn main() {
        // type mismatch: ... implements the trait `core::ops::Fn<(String,)>`,
        // but the trait `core::ops::Fn<(usize,)>` is required
        // [E0281]
        foo(|y: String| { });
    }

The issue in this case is that `foo` is defined as accepting a `Fn` with one argument of type `String`, but the closure we attempted to pass to it requires one arguments of type `usize`.