Macro validate_arg_count 

macro_rules! validate_arg_count {
    ($args:expr, $name:expr, $exact:expr) => { ... };
    ($args:expr, $name:expr, $min:expr, $max:expr) => { ... };
}

Macro to validate argument count for scalar functions.

Usage

// Exact count
validate_arg_count!(args, "UPPER", 1);

// Range (min, max inclusive)
validate_arg_count!(args, "SUBSTRING", 2, 3);