Re3: Optimizing a string processing sub

The @{[]} is a trick to force list context. The reason why list context is important is because of what the regex operator returns. In list context, the regex operator returns a list of what is matched. In scalar context, the regex operator returns whether or not it matched. (In theory, that should be the number of things matched as well, but I couldn't get it to work.)

So, by forcing list context, I get the list of things matched. Then, by converting the list to scalar context, I get the number of things in the list.

I'm sure there's a more elegant way than creating two array references on the fly, but that's what I had in 60sec of imperfect memory.

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

Comment on Re3: Optimizing a string processing sub Download Code

Replies are listed 'Best First'.
Re: Re3: Optimizing a string processing sub by sauoq (Abbot) on Jan 08, 2003 at 21:27 UTC
The `@{[]}` is a trick to force list context. Actually, it does a bit more than that. It creates an array. You could have forced list context simply by using parens but a list in scalar context would return the last element in the list rather than the number of elements. So, you did what you had to. :-) -sauoq "My two cents aren't worth a dime.";	[reply] [d/l]
Re: Re3: Optimizing a string processing sub by chromatic (Archbishop) on Jan 08, 2003 at 22:02 UTC
chromatic's context chaining: `my $count = () = $x =~ /(foo)/g;` Update: I'm not claiming to have originated it; I just liked the alliteration.	[reply] [d/l]
Re: Re3: Optimizing a string processing sub by MarkM (Curate) on Jan 08, 2003 at 22:04 UTC
To ensure that characters such as '^', '-' or ']' do not interfere, I would always be tempted to surround the interpolated value with \Q..\E. An alternative (more intuitive?) method of forcing list context on an expression, is to assign the expression to a list: `my $count = () = $x =~ /[\Q$y\E]/g;` The comma operator in scalar context returns the second argument. The intermediate assignment above causes the comma operator to believe it is an list context. UPDATE: chromatic beat me to the draw by 2 minutes on the ()= trick. However -- chromatic: you cannot claim credit for being the first to use this trick (chromatic's context chaining). I remember it from the time that it was being argued over on the perl5-porters mailing list, perhaps 5 years ago... :-)	[reply] [d/l]