Can we strict the subroutine in perl to receive number of arguments ?

Runtime? Compile time? Is @a considered to be one argument, or as many arguments as @a has elements?

Runtime is easy:

sub foo {
    unless (@_ <= 4) {
        die "foo allows at most 4 arguments";
    }
    ...
}
[download]

Compile time, you can do:

sub foo (;$$$$) {
    ...
}
[download]

The disadvantage of the latter is that it evaluates all the arguments to the sub in scalar context, and hence there's no flattening of lists. That is,

@bar = qw[red blue green yellow brown pink];
foo @bar;
[download]

is not an error - it calls foo with a single argument, 6; the number of elements in @bar.