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Re^10: Using 'keys' on a list (prototype & backwards compatibility)

by LanX (Sage)
on Jul 01, 2021 at 12:56 UTC ( #11134538=note: print w/replies, xml ) Need Help??


in reply to Re^9: Using 'keys' on a list (update x2)
in thread Using 'keys' on a list

all your code examples are broken (multiply) and don't compile.

At the same time you claim the output is factual.

Please don't do this!!!

Point is that keys' prototype expects one %hash or @array not a scalar.

And the argument must start with % or @

DB<20> p prototype "CORE::keys" \[%@] DB<21> p keys @a DB<22> p keys %a DB<23> p keys $a Experimental keys on scalar is now forbidden at (eval 32)[c:/Strawberr +y/perl/lib/perl5db.pl:738] line 2. Type of arg 1 to keys must be hash or array (not scalar dereference) a +t (eval 32)[c:/Strawberry/perl/lib/perl5db.pl:\ 738] line 2, at EOF DB<24>

The point you should make is that there has to be exactly ONE argument!

That's why keys can't expect a LIST.

and this can't be changed with a new feature, because otherwise old code would break.

Consider

@all_keys = keys %h1, keys %h2;

which will parse like

@all_keys = keys(%h1), keys(%h2);

and collect the keys from %h1 and %h2

DB<26> %h1=(a=>1) DB<27> %h2=(b=>2) DB<28> x @all_keys = keys %h1, keys %h2 0 'a' 1 'b' DB<29>

Now, if keys LIST was allowed, than the first keys would try to consume the rest of the list.

@all_keys = keys( %h1, keys(%h2) );

That's why the idea of the OP can't be implemented, without breaking backwards compatibility!

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

Replies are listed 'Best First'.
Re^11: Using 'keys' on a list (prototype & backwards compatibility)
by glycine (Sexton) on Jul 01, 2021 at 13:41 UTC

    OK, I had no idea why keys work so before.

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