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Re: Re (2): Hash/Array of Regular Expressions? (code)

by risacher (Beadle)
on Jun 24, 2001 at 20:41 UTC ( [id://91077]=note: print w/replies, xml ) Need Help??


in reply to Re (2): Hash/Array of Regular Expressions? (code)
in thread Hash/Array of Regular Expressions?

Since you've called me out by name, I guess I have to respond. And I wouldn't call myself a "frenzied map lover". Like any function, map has it's place.

When is the proper time to use map? I would argue that one should use map whenever you want to apply an expression to all the members of an array, and actually intend to use the array of results.

Map is contraindicated when you're not going to use the result... use foreach in that case; map adds extra overhead compared to foreach if you aren't going to use the result. (that's the only additional overhead that I know of.) In this case, bikeNomad is using the result, and the code is therefore concise, and correct.

Dep, you haven't shown any reason why map is a bad idea in this case. I think that clarity here is achieved by separating out the array of regexps, so that they are visually distinct and clear. Then, the code that maps that with qr() is also visually separate. I think this is a good thing.

Since you implied you wanted it, here's my stylistic criticism of your alternatives:

@array = ( qr{^abcd}, qr{cd[ef]g}, qr{cat$} );

Putting a qr{} around each search term is terrible, IMHO. If you had a list with many search terms, it would result in much more typing. Even with a few terms, it means that each search expression that the author is trying to express is wrapped in a little bit of ugliness. (I do appreciate your use of qw{} elsewhere, to reduce quotes.)

foreach ( qw{ ^abcd cd[ef]g cat$ } ) { push @array, qr{$_} }

This isn't bad, but recommending it is the same as saying that map() shouldn't exist, since it's exactly the same, except with more typing.

 push @array, qr{$_} for qw{ ^abcd cd[ef]g cat$ };

This is worst of all, I think, because it relies on the wierd semantic order of things in perl that few other languages implement (like putting the loop conditions after the loop body). Don't get me wrong, I think that sort of thing is cool, and is great for a some circumstances. But really, the point of the backwards syntax is to make perl read more like English. I'd rather my perl code read like C or TCL or lisp than English. Those types of constructs are exactly the sorts of things that make perl hard to read for novice perl programmers. The fact that I can iterate the push after-the-fact like you suggest here is non-obvious to someone coming from another language. Even someome familiar with perl might wonder, whether the precedence rules will do what you want. As it turns out, your code is correct, of course. But someone could easily read it as meaning something like: push @array, { qr{$_} } for qw{ ^abcd cd[ef]g cat$ };, which, of course, is wrong.

My own stylistic fetishes, aside, you never said what you thought was wrong with using map. What is it that you object to?

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