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Understanding and Fixing Rust Error E0593

Overview of Rust Error E0593

Rust Error E0593 occurs when you attempt to supply an Fn-based type with an incorrect number of arguments than what was expected. This can lead to a type mismatch or a failure to satisfy trait bounds which ultimately results in a compile-time error.

In this article, we will discuss the root cause of Rust Error E0593, examine code examples that trigger the error, and provide solutions to fix the issue.

Erroneous Code Example

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

fn main() {
    // [E0593] closure takes 1 argument but 0 arguments are required
    foo(|y| { });
}

In the above example, the function foo() accepts a closure with an Fn-based type as a parameter. It expects a closure that takes zero arguments, but we have passed a closure that takes one argument (|y| {}). This leads to Rust Error E0593.

Fixing Rust Error E0593

To fix Rust Error E0593, we need to ensure that the closure provided to the function has the same number of arguments as expected by the Fn-based type. If there's a mismatch, adjust the closure to match the expected type.

Corrected Code Example

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

fn main() {
    foo(|| { }); // ok!
}

In this corrected example, we have replaced the closure that takes one argument (|y| {}) with a closure that takes zero arguments (|| {}). This resolves the issue and the code will now successfully compile.

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