array append result type

[Ali Çehreli via Digitalmars-d-learn]

On 10/06/2014 04:40 AM, monarch_dodra wrote:
> On Monday, 6 October 2014 at 11:28:16 UTC, John Colvin wrote:
>> string a;
>> char[] b;
>> pragma(msg, typeof(a ~ b)); // char[]
>>
>> why not string?
>>
>> What are the rules that determine this?
>
> *Ideally*, I'd have said "it returns char[], so that you can chose via
> purity".
>
> However, it's not pure, so that argument doesn't hold.

Array concatenation should be considered pure because it is the 
equivalent of the following function, which currently works:

pure char[] cat(string a, const(char)[] b)
{
     return a ~ b;
}

void main()
{
     string a;
     char[] b;

     char[] c = cat(a, b);    // works
     string s = cat(a, b);    // works
}

   http://dlang.org/function.html#pure-functions

We should bring the above function and the ~ operator in line with each 
other. I haven't followed the discussions on GC usage in purity closely 
but if 'new' is allowed, GC allocations should be allowed as well.

Ali