Re: Perl Idioms Explained - !!expr

[Anonymous Monk]

Can you comment on the alternatives?

return grep { $_ eq $_[0] } @_[ 1 .. $#_ ];

# or

return ~~grep { $_ eq $_[0] } @_[ 1 .. $#_ ];

# or

my $searched = shift;
return !!grep { $_ eq $earched } @_;

Should I use them? And if not, why?

Thanks

[broquaint]

  return grep { $_ eq $_[0] } @_[ 1 .. $#_ ];

Depending on context this will return different things, whereas !!expr will always return a boolean value.

  return ~~grep { $_ eq $_[0] } @_[ 1 .. $#_ ];

This will return the number of elements returned by grep as opposed to !!expr which, again, will return a boolean value.

Of course both of the above are valid in appropriate situations, but if you just want a boolean value then !!expr is an appropriate idiomatic solution.

[japhy]

I like ~~EXPR as a brief (read: obfuscated) way to enforce scalar context on an expression; it only renders the return value unusable if EXPR is a reference.

[davidrw]

I would also mention just a simple ternary operator as an alternative:

return grep($_ eq $_[0], @_[ 1 .. $#_ ]) ? 1 : '';

or, more generally the equivalent to !!$expr is (some of the parens are optional depending on context):

(($expr)?1:'')