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Re: Contents of @_ using subroutine signatures with default values (not a bug)

by LanX (Sage)
on Jul 14, 2020 at 12:16 UTC ( #11119298=note: print w/replies, xml ) Need Help??


in reply to Contents of @_ using subroutine signatures with default values

Hi David,

I'm not sure if I understand your problem ...

... the call foo("a") is exactly doing what I expect, i.e. @_ == 1

Anything else - like pushing an optional $that into @_ - wouldn't really be backwards compatible.

And the number you seem to want is static, it's the sum of obligatory arguments + defaulted ones.

(maybe you want to make a feature request to be able to introspect the signature)

FWIW, when interested you can look into the implementation with B::Deparse ...

# https://perlmonks.org/?node_id=11119273 use strict; use warnings; use feature qw(signatures); no warnings qw(experimental::signatures); use B::Deparse; use Test::More; sub foo ($this, $that='bar') { return scalar @_; } is( foo(1), 1, "one arg" ); is( foo(1,2), 2, "two args" ); done_testing(); warn "Show implementation:\n", B::Deparse->new()->coderef2text(\&foo);

C:/Perl_524/bin\perl.exe -w d:/exp/pm_signatures.pl ok 1 - one arg ok 2 - two args 1..2 Show implementation: { BEGIN {${^WARNING_BITS} = "\x54\x55\x55\x55\x55\x55\x55\x55\x55\x5 +5\x55\x55\x55\x55\x54\x55\x05"} use strict; use feature 'signatures'; die sprintf("Too many arguments for subroutine at %s line %d.\n", +(caller)[1, 2]) unless @_ <= 2; die sprintf("Too few arguments for subroutine at %s line %d.\n", ( +caller)[1, 2]) unless @_ >= 1; my $this = $_[0]; my $that = @_ >= 2 ? $_[1] : 'bar'; (); return scalar @_; } at d:/exp/pm_signatures.pl line 32. Compilation finished at Tue Jul 14 14:25:41

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

UPDATE

expanded code with tests

Replies are listed 'Best First'.
Re^2: Contents of @_ using subroutine signatures with default values
by LanX (Sage) on Jul 14, 2020 at 13:01 UTC
    a more sophisticated test, covering errors too
    # https://perlmonks.org/?node_id=11119273 use strict; use warnings; use feature qw(signatures); no warnings qw(experimental::signatures); use B::Deparse; use Test::More; sub foo ($this, $that='bar') { return scalar @_; } t_foo(0,undef,'Too few arguments'); t_foo(1,1,"One arg"); t_foo(2,2,"Two args"); t_foo(3,undef,"Too many arguments"); done_testing(); sub t_foo { my ($n_args, $exp, $desc ) = @_; my @args = ("","a".."z")[1..$n_args]; my $code = "foo(qw/@args/)"; my $got = eval $code; unless ($@) { is( $got, $exp, "<$code> \t $desc: \@_ == $got" ); } else { ok( $@ =~ $desc, "<$code> \t ERR: $desc: "); } } #diag "Show sig implementation:\n", B::Deparse->new()->coderef2text(\& +foo);

    C:/Perl_524/bin\perl.exe -w d:/exp/pm_signatures.pl ok 1 - <foo(qw//)> ERR: Too few arguments: ok 2 - <foo(qw/a/)> One arg: @_ == 1 ok 3 - <foo(qw/a b/)> Two args: @_ == 2 ok 4 - <foo(qw/a b c/)> ERR: Too many arguments: 1..4

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery

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