Why are these C++ headers specified to include ?

Question

As can be seen from https://stackoverflow.com/a/26614984/481267 the following headers are guaranteed by the standard to #include <initializer_list>:

Everything in [containers]
<utility>
<string>
<algorithm>
<random>
<valarray>
<regex>

Most of these headers declare at least one function that takes a std::initializer_list<E> argument, so it makes sense. However,

<array>, <stack>, and <queue> have no such functions, although perhaps it makes sense to treat all containers uniformly here.
<utility> has no such functions.
<iterator> does have functions with an initializer_list argument (rbegin, rend) but it's not specified to include <initializer_list>.

What is the rationale behind these exceptions?

I think even using uniform initialization requires the inclusion of ``. See the comments of this question [here](http://stackoverflow.com/q/33704978/3093378). — vsoftco, Jun 06 '16 at 23:20
The inclusion in `` dates all the way back to N2672. The rest are done by N2930. Free `rbegin`/`rend` are late additions. — T.C., Jun 06 '16 at 23:37
@vsoftco Only if you make use of the type explicitly or implicitly. — T.C., Jun 06 '16 at 23:38
@T.C. That's true, e.g. for something like `auto x = {1,2,3};`, but probably code like this doesn't appear in the standard library. — vsoftco, Jun 06 '16 at 23:39
@Yakk Most of this predates git, actually. Just did a binary search of old working drafts. — T.C., Jun 07 '16 at 10:48

score 1 · Answer 1 · answered Dec 27 '16 at 19:47

Seems like there is no explicit rationale, just that some proposals for additions to the standard were made and those proposals were accepted.

At the very end of the document N2672 Initializer List proposed wording it just says:

In 20.2 Utility components [utility] paragraph 1:

This subclause contains some basic function and class templates that are used throughout the rest of the library.

Header <utility> synopsis
     #include<initializer_list>
      namespace std {

So, the authors of the paper saw initializer_list as a utility, and so it ought to be included with the <utility> header. And therefore it is.

The paper didn't propose any changes to the <iterator> header, so none were made.

Why are these C++ headers specified to include ?

1 Answers1