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April 02, 2021
Gravatar of Per NordlöwPosted by Per Nordlöw
in reply to Ali Çehreli		Reply
Per Nordlöw
Gravatar of Per Nordlöw
Posted in reply to Ali Çehreli


Reply

On Thursday, 1 April 2021 at 23:21:56 UTC, Ali Çehreli wrote:

>

As I mentioned elsewhere in this thread, the element type must not have indirections though. If S is a struct with indirections, concatenating const(S)[] should still produce const(S)[].

Thanks.

Got something working that allows the implicit conversion at

https://github.com/dlang/dmd/pull/12341

for the sample code

@safe pure unittest
{
    const(char)[] x;
    string y;
    string z1 = x ~ y; // now passes
    string z2 = y ~ x; // now passes
}

but nothing else.

Feel perfectly free to fill in the details or even take over the PR.

April 02, 2021
Gravatar of Steven SchveighofferPosted by Steven Schveighoffer
in reply to H. S. Teoh		Reply
Steven Schveighoffer
Gravatar of Steven Schveighoffer
Posted in reply to H. S. Teoh


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On 4/1/21 6:55 PM, H. S. Teoh wrote:
> On Thu, Apr 01, 2021 at 06:34:04PM -0400, Steven Schveighoffer via Digitalmars-d wrote:
> [...]
>> ```d
>> auto concat(T, U)(T[] x, U[] y) pure
>> {
>>      return x ~ y;
>> }
>>
>> void main()
>> {
>>      string x;
>>      const(char)[] y;
>>      string z = concat(x, y); // compiles
>> }
>> ```
> [...]
> 
> Put this way, the solution becomes obvious: `~` should be considered a
> pure operation.  Then the compiler (in theory) ought to be able to
> infer uniqueness from `x ~ y`, and consequently allow implicit
> conversion to immutable.

It is considered pure, note that I'm using concatenation inside the function (which is marked pure).

-Steve
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