foreach ref very broken: fails to call front(val)

[Andrei Alexandrescu]

On 7/10/12 4:29 AM, kenji hara wrote:
> Posted a pull request:
> https://github.com/D-Programming-Language/phobos/pull/678

Hmm, that has a couple of issues.

First, map that modifies things in place is a bug more often than a 
feature given that the caller of map may use front() an arbitrary number 
of times. So I see little intentional and legitimate use for things like 
map!"a += 2"(range).

Second, the return by value from Array is intentional and has to do with 
sealing. Array is intended to never escape the addresses of its 
elements. That way, the collection is "sealed" in the sense there can 
never be uncontrolled pointers to its elements. This allows using 
efficient allocation strategies for the array without compromising its 
safety.

In more recent discussions with Walter we discussed the possibility of 
making "ref" returns transitory, i.e. no caller code can actually save a 
ref result beyond the call. That would allow us to keep sealing while 
also benefitting of ref returns. But that feature has not been 
implemented yet.


Andrei