Error code E0057

An invalid number of arguments was given when calling a closure.

Erroneous code example:

#![allow(unused)] fn main() { let f = |x| x * 3; let a = f(); // invalid, too few parameters let b = f(4); // this works! let c = f(2, 3); // invalid, too many parameters }

When invoking closures or other implementations of the function traits Fn, FnMut or FnOnce using call notation, the number of parameters passed to the function must match its definition.

A generic function must be treated similarly:

#![allow(unused)] fn main() { fn foo<F: Fn()>(f: F) { f(); // this is valid, but f(3) would not work } }