Default struct constructor

[Ali Çehreli]

On 1/27/21 2:05 PM, Paul wrote:

 > Does this mean opCall takes priority over default constructors (or
 > struct literals

Assuming static opCall is defined, there are two syntaxes:

S a;        // Equals S.init; no constuctor run
S b = S();  // static opCall; no constuctor run

foo(S());     // static opCall
foo(S.init);  // S.init

 > I have no clue what the difference is, semanthically or
 > implementation wise), whilst it does not when arguments are included?

I don't know; let's try. :)

import std.stdio;

struct S {
   this(int) {
     writeln("ctor");
   }

   static opCall(int) {
     writeln("opCall");
     S s;
     return s;
   }
}

void foo(S) {
}

void main() {
   auto a = S(1);
   foo(S(2));
}

Both of the calls in main go to this(int); opCall is ignored.

 > By the way, doesnt this mean a this(){} syntax could be implemented by
 > treating it as syntactic sugar for opCall?

Being able to define a default constructor and then saying we don't have 
default constructors would be confusing I think.

 > I noticed C++ also has
 > non-argument struct constructors, so its a bit curious to me.

Those are called default constructors. D thinks it differently: there 
are no default constructors for strtucts. opCall is a strange thing 
where the name of the type is callable and it looks like a default 
constructor in usage.

Ali