[boost] Re: Formal Review: FOREACH macro

From: Andrei Alexandrescu (See Website For Email) (SeeWebsiteForEmail_at_[hidden])
Date: 2005-05-02 23:43:08

>>I see some of them as friends. Macros in general (and FOREACH in 
>>particular) are in most cases only usability helpers (there is also 
>>configuration switched domain, but it's beside the point). And until 
>>language provide as-convenient alternatives I am ready to accept the 
>>macro nature of these tools.
> 
> 
> I'm ready to accept them too, when they do something worth while. This one 
> doesn't.

Well, IYO :o). IMO it does. There are two things that give FOREACH an 
advantage: (1) optional immutability of the value being iterated (and, 
to my happiness, less syntax means more safety! yay!); (2) immutability 
of the iterator itself.

Statistically---but please don't make me dig a reference to that one 
:o)---most bugs are due to loops. The C for loop is the most general 
loop; that's what also makes it the least structured. The fact that the 
loop control sits in the header of the for statement is only a mere 
convention, and, sadly, often an illusion to the beginner, unwary, or 
maintainer :o). In contrast, FOREACH's header makes a much stronger 
statement about the nature of the loop, and that brings structure. You 
look at a line of code and you have some pretty good assurance about the 
nature of the loop. That's where IMHO most of its value comes from.

Syntactic convenience is a good artifact, but it should be seen as not 
much more than a fringe benefit.

Andrei