Classes in D and C++

[Frits van Bommel]

Bill Baxter wrote:
> Lionello Lunesu wrote:
>>
>> Instead of a constructor, create a "static opCall". opCall is the 
>> overload for "(..)" so you can instantiate your type similar to C++:
>>
>> struct SomeType {
>>   int member = 0;// default initializer here
>>   static SomeType opCall( int whatever ) {
>>     SomeType st;
>>     st.member = whatever;//custom initialize
>>     return st;
>>   }
>>   //...
>> }
>>
>> SomeType st = 2;//construction
>>
>> No need for constructors ;)
> 
> I don't think that quite works as you wrote.
> I think it needs to be
>    SomeType st = SomeType(2);
> or
>    auto st = SomeType(2);
> 
> if you want to avoid repeating your repeat-avoiding self repeatedly.

Actually, with a slight modification that compiles just fine:
---
struct SomeType {
   int member = 0;// default initializer here
   static SomeType opCall( int whatever ) {
     SomeType st;
     st.member = whatever;//custom initialize
     return st;
   }
   //...
}

void main() {
     SomeType st = 2;//construction
}
---
Static opCall isn't compile-time executable since it uses a struct :(, 
so the declaration must be in a function. (This is actually a pretty 
good argument to allow compile-time execution to work with structs, I think)

This has been allowed for a while now, see 
http://www.digitalmars.com/d/changelog2.html#new0177 :
---
# Casting a value v to a struct S is now rewritten as S(v).
# Initializing a struct S from a value v is now rewritten as S(v).
---