And that is something I don't understand. What makes map so special? Any function in Perl will return something, be it a buildin or a user defined sub, and even operators return values. Why is it that people get all confused if they see a map in void context, and start looking where the return value goes, but they don't have problems with other functions?

What makes map so special?

Map is special, in my opinion, because there is a nearly analogous construct which does not return values.

Good style involves choosing appropriate tools. Given a situation where no return value will be used, I tend to expect someone to pick the tool which returns no value... unless there is a good reason to do otherwise. Forcing list context, for example.

If I see someone make a different choice, I will wonder why, and I will investigate. If, at the end of my investigation, I conclude that the author could have used a foreach loop just as effectively, I will be annoyed. By passing up the more appropriate (and more obvious) tool, he has obliged me to go looking for something subtle which was not there. Likewise, I wouldn't expect a person to choose

() = do_something ($_) for @some_list;

over

do_something ($_) for @some_list;

unless there was actually a need to force list context; if the author consistenly chose the former as his idiom without good reason, I'd find it very irritating (though not half so irritating as an author who inconsistently chose this, or map in void context, without good reason).

On the other hand, perhaps the author intends to alert me to the significance of context here. Saying

would then be a louder hint, and I'd generally prefer it; but if the author was consistent in using map for this purpose, I wouldn't call it bad style. I might appreciate a note somewhere, as this is not common practice.

An author might choose map for this, I think, on the grounds that he was choosing the most appropriate tool. In a very fastidious author, whose code was so clean and consistent that it gave the reader a sense of confidence that each thing was as it was for a reason, this might be a bit of minimalism which I would admire. However I would be surprised to see such a person call his own functions in such a fashion, because I wouldn't expect him to write a function which altered its arguments differently depending on the context in which it was called. I cannot think of a good reason to do this.