perl function prototype

The prototype function in Perl is used to get or set the prototype of a named subroutine. The prototype of a subroutine is a special kind of syntax that is used to define the types and number of arguments that the subroutine expects.

Here's the syntax for the prototype function:

prototype $subroutine_name;
prototype $subroutine_name $prototype;

The first form returns the current prototype of the specified subroutine, if any. The second form sets the prototype of the specified subroutine to the specified prototype, if any.

Here's an example that shows how to use the prototype function to set the prototype of a subroutine:

sub add_numbers($$) {
    my ($num1, $num2) = @_;
    return $num1 + $num2;
}

print add_numbers(1, 2);   # prints 3

my $proto = prototype("add_numbers");
print "Prototype before: $proto\n";   # prints "Prototype before: "

# Set the prototype to take two scalar arguments
prototype("add_numbers", "\$\$");

$proto = prototype("add_numbers");
print "Prototype after: $proto\n";   # prints "Prototype after: $$"

print add_numbers(1, 2);   # prints 3

In this example, we define a subroutine add_numbers that takes two scalar arguments and returns their sum. We then call the prototype function to get the current prototype of the add_numbers subroutine, which is an empty string because we haven't set a prototype yet. We then use the prototype function to set the prototype of the add_numbers subroutine to take two scalar arguments. Finally, we call the add_numbers subroutine again with two scalar arguments, and this time it works as expected because the prototype is set correctly.