• Patric Dexheimer (20/20) May 05 2017 struct Base(T){
• Adam D. Ruppe (19/25) May 05 2017 You should never use static opCall. They are ambiguous with
• Patric Dexheimer (5/12) May 05 2017 It make sense. Even liking of the possibilities of static opCall.

Patric Dexheimer <patric.dexheimer gmail.com> writes:

struct Base(T){
	static T opCall(Args...)( Args args ){
		writeln(args);
		writeln("opCall");
		T t;
		return t;
	}
}

struct Data{
	Base!Data b;
	alias b this;
}

void main()
{	
         // Expected: opCall of Base!Data, but get error
	// auto x = Data(10);
         // opCall called. What just happened here?
         // never saw anything about init as function.
	auto y = Data.init(10);
}

Adam D. Ruppe <destructionator gmail.com> writes:

On Friday, 5 May 2017 at 13:05:35 UTC, Patric Dexheimer wrote:
 	static T opCall(Args...)( Args args ){

You should never use static opCall. They are ambiguous with 
non-static opCall as well as with constructors. It is a buggy 
mess that should never have been in the language in the first 
place.

         // Expected: opCall of Base!Data, but get error
 	// auto x = Data(10);
         // opCall called. What just happened here?

It is ambiguous with a constructor call on Data. It is trying to 
construct a Data, but there's not applicable constructor so it is 
an error. Note that alias this NEVER applies to constructors (and 
since static opCall is ambiguous with constructors, that doesn't 
work either), but only works on existing objects.

         // never saw anything about init as function.
 	auto y = Data.init(10);

T.init is an existing value used to initialize any type, so it is 
no longer a constructor and can call operator overloads....

But, while this should be a non-static opCall, static opCall will 
hijack that too.


Your short code hit the two big reasons why static opCall ought 
to be deprecated and totally removed: it gets confused for ctors 
and non-static opCalls, breaking in situations where you think it 
would be them, and cannot coexist with them either.

I suggest you find some other way entirely to write the code.

Patric Dexheimer <patric.dexheimer gmail.com> writes:

On Friday, 5 May 2017 at 13:19:03 UTC, Adam D. Ruppe wrote:
 On Friday, 5 May 2017 at 13:05:35 UTC, Patric Dexheimer wrote:
 [...]

 You should never use static opCall. They are ambiguous with 
 non-static opCall as well as with constructors. It is a buggy 
 mess that should never have been in the language in the first 
 place.

 [...]


It make sense. Even liking of the possibilities of static opCall.
But I believe that somethings must exist to evade opCall usages 
now
like empty params ctor on structs.