On Monday, 15 February 2016 at 22:48:16 UTC, Walter Bright wrote:
rears its head again :-)
Head Const is what C++ has for const, i.e. it is not
transitive, applies to one level only. D has transitive const.
What head const will do for us:
1. make it easy to interface to C++ code that uses const, as
currently it is not very practical to do so, you have to resort
to pragma(mangle)
2. supports single assignment style of programming, even if the
data is otherwise mutable
The downside is, of course, language complexity.
I'll leave to others to discuss whether a language solution is
worth it, but I just wanted to point out there are two library
solutions in this area:
HeadConst [1] - PR pending, and
Rebindable (tail const) [2] - already part of Phobos.
Maybe if the language could express head const, it also makes
sense to have tail const.
[1]: https://github.com/D-Programming-Language/phobos/pull/3862
[2]:
http://dlang.org/phobos-prerelease/std_typecons.html#.Rebindable
