Too few type arguments were supplied for a function. For example:
fn foo<T, U>() {}
fn main() {
foo::<f64>(); // error: wrong number of type arguments: expected 2, found 1
}Note that if a function takes multiple type arguments but you want the compiler to infer some of them, you can use type placeholders:
fn foo<T, U>(x: T) {}
fn main() {
let x: bool = true;
foo::<f64>(x); // error: wrong number of type arguments:
// expected 2, found 1
foo::<_, f64>(x); // same as `foo::<bool, f64>(x)`
}