this() in struct

[Ali Çehreli]

On 10/09/2012 10:08 AM, Zhenya wrote:
> On Tuesday, 9 October 2012 at 17:21:47 UTC, Zhenya wrote:
>> Hi!
>> I'm sorry,maybe this topic already was discussed,but could anybody
>> explain me
>> why default constructor was disallowed in structs?
>
> And if I have to do some initialization of data members,what is the way
> to do it?

I am not sure about the rationale myself. This issue is being discussed 
at the main D forum:

   http://forum.dlang.org/thread/fgldbozuneoldxjrwxje@forum.dlang.org

Here is what I know: If the initial values are the same for all objects, 
then use initial values:

struct S
{
     int i = 42;
     double d = 1.5;
}

If you do not want to keep the initial values or they are not available 
at compile time, then you can use a 'static opCall':

struct S
{
     int i;
     double d;

     static S opCall()
     {
         S result;
         result.i = 43;
         result.d = 2.5;
         return result;
     }
}

void main()
{
     auto s = S();
}

But then that opCall gets in the way and you can't write the following 
any more:

     auto s = S(44, 5.5);
/*
   Error: function deneme.S.opCall () is not callable using
          argument types (int,double)
   Error: expected 0 arguments, not 2 for non-variadic function
          type S()
*/

It still resolves to the static opCall even though the parameters don't 
match.

Ali