BOOST_FOREACH: A Bad Implementation of a Good Idea

I am more and more often running across constructs, especially from boost, that I find to be intuitively poor.

BOOST_FOREACH is the latest one that I've looked at.

First let me state that I like the concept of for each as is implemented in many languages. C++ doesn't happen to implement it and some really smart people decided that it would be cool to create something that has the expressive niceties of for each.

One result is BOOST_FOREACH. However, the include file runs to over 67,000 lines of code and in my opinion the readability is worse.

Why?

Consider the following snippet.

BOOST_FOREACH(T & a, myClass.getAVector()) {

foo(a);

}

Here is another way to write it:

T &aVec = myClass.getAVector();

for(std::vector::iterator it = aVec.begin(); it != aVec.end(); ++it) {

foo(a);

}

And another which is more like std::for_each:

T &aVec = myClass.getAVector();

std::vector::iterator begin = aVec.begin();

std::vector::iterator end = aVec.end();

for(std::vector::iterator it = begin; it != end; ++it) {

foo(a);

}

Which is easier to understand?

Is the invariant getAVector() removed from the loop?

Is end called for each loop or once at the beginning like std::for_each?

Did you know that std::for_each is more like my second example than the first?

If there is a side-effect of calling getAVector() what is the behavior?

What happens if the size of the container changes during the loop?

Is the expanded macro efficient?

Can everyone on your team answer these questions?

Can new developers that may come into your team answer these questions?

Should we spend 67,000 lines of extra code for every compilation unit that uses BOOST_FOREACH to save a few dozen characters?

My conclusion is that BOOST_FOREACH is not more readable and the cost is not worth the header load even if it were.

I will not be using it.