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From: Edward Diener (eddielee_at_[hidden])
Date: 2005-05-02 19:34:16

Andrei Alexandrescu (See Website For Email) wrote:
> Paul Mensonides wrote:
>> I'll reiterate something that you said a while back (paraphrasing). The
>> greatest harm that the macro mechanism (in C/C++) has caused is that
>> it has kept
>> people from realizing the benefits of syntactic abstraction.
>> Furthermore, whether something is or isn't a macro is irrelevant. It
>> is whether
>> it provides a useful abstraction that is documentable. As a macro,
>> the name is
>> not going to collide with anything because of all-caps and the BOOST_
>> prefix.
>> Similarly, it isn't going to accidentally expand in any code. As I've
>> said
>> before (paraphrasing), macro invocations are nothing like function
>> calls except
>> in appearance, and nearly all other macro-related problems stem from
>> developers
>> viewing them as if they are. Macros' "return values" are code
>> snippets, not
>> values. E.g.
>> #define max(a, b) ((a) < (b) ? (b) : (a))
>> The problem here is not that 'max' has a problem with multiple
>> evaluation; the
>> problem is that typical developers view 'max' as returning either 'a'
>> or 'b'.
>> In other words, whether an abstraction is a macro is an important
>> documentation
>> point, and the documentation of an abstraction, regardless of what it
>> is (macro,
>> function, class, etc.), dictates the entirety of how it is to be used.
> Agreed. In the case of max, it's the syntactic similarity with a
> function call that lures people into making certain assumptions. Same
> goes about non-macro entities such as auto_ptr - "a = b;" looks like
> something that ain't.
> By the way, it was FOREACH that inspired me to figure out a simple
> solution to max, which then Eric improved. It's basically like this:
> #define max(a, b) (max_fn(true ? (a) : (b), false ? (a) : (b)))
> which presto, nice-o passes the appropriate types to a template max_fn
> function that now can be smart about returning lvalues and so on.

You have stumped me here. Why does one not do:

#define max(a, b) (max_fn((a),(b))

instead ?

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