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Re: Chaining string ops

by asarih (Hermit)
on Aug 28, 2003 at 18:14 UTC ( #287478=note: print w/replies, xml ) Need Help??


in reply to Chaining string ops

If I understand you correctly, you want to say
$str = "the boy walked the dog"; $str =~ s/walked/fed/ =~ s/boy/girl/ =~ s/dog/Audrey II/; # error
Here's why it shouldn't work. Since s/// returns a number of times a match is found, anyway you associate =~, you end up with something like
$str =~ 1
at some point. This is not legal. If you want to chain =~, then we must expect s/// to return a string.

Specifically, we must get one that does regular expressions such as s/this/that/ or m[^/usr/local/bin], but then this prohibits us from saying

if ($str =~ s/boy/girl/) { # do this }
because the condition will evaluate to false. I'd rather have if ( $s =~ /match/ ) { .. } rather than the chain-ability of s///.

Update: Above discussion assumes that =~ is right associative, but in fact it is left associative. This means that as long as =~ returns an integer, we have a trouble (say 1=~ s/this/that/). I like roju's idea of returning a string, but I don't know how easy/hard it is to implement it.

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Re: Re: Chaining string ops
by roju (Friar) on Aug 28, 2003 at 19:25 UTC
    Could we not have it both ways? After all, this is perl....

    if ($s =~ s/change/me/)
    and
    $str = "some string" =~ s/a/b/r =~ s/foo/bar/r

    where /r is the newly created "chaining" modifier that forces a /r/eturn of the new string. Make it have no side effects either (ie. not touch the original string), and it'd fill a need.

    Update: changed /c to /r, seeing as /c is taken.

Re: Re: Chaining string ops
by traveler (Parson) on Aug 28, 2003 at 19:30 UTC
    Yes. I understand this. The question is which is more useful: returning the number of matches, or returning the changed string? Both are useful! I like roju's suggestion of a new string modifier.

    --john

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