You want to use function prototypes so the compiler can check your argument types.
Perl has something of a prototype facility, but it isn’t what
you’re thinking. Perl’s function prototypes are more like
a context coercion used to write functions that behave like some of
Perl’s built-ins, such as
Manually checking the validity of a function’s arguments can’t happen until run-time. If you make sure the function is declared before it is used, you can tickle the compiler into using a very limited form of prototype checking to help you here. Don’t confuse Perl’s function prototypes with those found in any other language. Perl prototypes serve only to emulate the behavior of built-in functions.
A Perl function prototype is zero or more spaces, backslashes, or type characters enclosed in parentheses after the subroutine definition or name. A backslashed type symbol means that the argument is passed by reference, and the argument in that position must start with that type character.
A prototype forces context on the arguments to the prototyped
function call. This is done when Perl compiles your program, and in
most cases this does not necessarily mean that Perl checks the number
or type of the arguments to your function. If Perl sees
5) for a function
($), it will stop with a compile-time error. But
if it sees
func(@array) with the same prototype,
it will merely put
@array into scalar context instead ...