Macro check_arity 

macro_rules! check_arity {
    ($args:expr, $name:expr, $exact:literal) => { ... };
    ($args:expr, $name:expr, $lo:literal ..= $hi:literal) => { ... };
    ($args:expr, $name:expr, $lo:literal ..) => { ... };
}

Check arity of a native function’s arguments, returning SemaError::Arity on mismatch.

Forms

check_arity!(args, "fn-name", 2);        // exactly 2
check_arity!(args, "fn-name", 1..=3);    // 1 to 3 inclusive
check_arity!(args, "fn-name", 2..);      // 2 or more