How do I get the signature of a subroutine in runtime?

user_124486 0
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Perl provides an API via CORE::prototype, that allows you to get a prototype. This is further documented by Sub::Util which is the documented method for working with subs,

Sub::Util::prototype,

Returns the prototype of the given $code reference, if it has one, as a string. This is the same as the CORE::prototype operator; it is included here simply for symmetry and completeness with the other functions.

However, I don't see anything anywhere on how to get the signatures in runtime? Does perl make this available?

subroutine-prototypes signature subroutine perl metaprogramming
3 Answers

This is very ... indirect, but deparse the sub and parse the signature code.

sub foo ($bar) { return 0 }

use B::Deparse;
$foo = B::Deparse->new->coderef2text(\&foo);

# contents of foo:
# BEGIN {${^WARNING_BITS} = "\x10\x01\x00\x00\x00\x50\x04\x00\x00\x00\x00\x00\x00\x55\x50\x55\x50\x51\x01"}
# use feature 'signatures';
# die sprintf("Too many arguments for subroutine at %s line %d.\n", (caller)[1, 2]) unless @_ <= 1;
# die sprintf("Too few arguments for subroutine at %s line %d.\n", (caller)[1, 2]) unless @_ >= 1;
# my $bar = $_[0];
# return 0;

@foo = split /\n/, $foo;
if ($foo[2] =~ /use feature 'signatures'/ &&
        $foo[3] =~ /Too many arguments/ &&
        $foo[4] =~ /Too few arguments/) {
    @sig = ();
    $n = 5;
    do {
        ($sig) = $foo[$n] =~ /my (\W\w+) = /;
        push @sig,$sig if $sig;
        $n++;
    } while ($sig);
    print "Signature is (", join(",",@sig), ")\n";
}
user_1686570

This is currently not possible, for the same reason why traditional argument parsing (my ($foo, $bar) = @_;) isn't: it's internal to the subroutine.

It has been suggested before to add such a thing, but currently it doesn't appear to be likely.

Leon_Timmermans_47270

From irc.freenode.net/#perl,

15:03 < Grinnz> there's no perl level api for that

That's pretty much a perl demiboss. He pointed me to this work from Nov 2019 which starts down the path of "Signature introspection API."

user_1244860
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