On 7/30/16 5:21 PM, Q. Schroll wrote:
On Friday, 29 July 2016 at 19:24:59 UTC, Steven Schveighoffer wrote:
On 7/29/16 3:00 PM, Q. Schroll wrote:
Cases to consider: Arrays and AAs with const(T) Elements, where T is a
value or a reference type respectively.
[snip]
Questions:
(1) Why do I have to specify the type here? Why does inference fail?
(2) Why not just S[S]?
The copy of a const S is a S so why is the copy of a (const S, const
S)-pair not just (S, S)?
array.dup has the meaning to copy the original but make the elements
mutable. At least, that's what it was when it was handled by the
compiler/runtime.
I do understand the reasons why I can't simply copy const reference type
objects to mutable. It just makes sense as the referred object is still
const.
I thought of dup being there for convenience and performance reasons.
The spec says about dup: "Create a dynamic array of the same size and
copy the contents of the array into it."
It has not been clear to me it intends to make the elements mutable. For
my intention, I thought of dup making a shallow copy--which is a deep
copy on value types so it can drop the const then.
If that intention is not in the docs, then that is an omission. It
definitely always intends to make the result mutable, and should be an
error if you can't do that. Much code out there expects it to be this
way, and would break if it simply copied the const tag.
I went ahead and submitted a PR:
https://github.com/dlang/dlang.org/pull/1435
-Steve
