Re: hacky way to get explicit default constructor on struct :P

[Steven Schveighoffer via Digitalmars-d]

On 10/28/17 12:59 PM, LunaticWare wrote:
Event if there is no default constructor on struct we can still make one 
that work as well as if it were implemented, here is my example n__n

------

import std.format;
import std.stdio;

struct Player
{
     string name = "Baz";
     float[2] position = [0, 0];

     // Adding an explicit constructor to struct =)
     // But we can't enforce it since this relies on it =(
     static ref auto opCall(string name = "Bar", float x = 1, float y = 1)
     {
         // Even if we give no argument opCall will still be called ;)
         writefln("Entering the explicit constructor as '%s'", name);

         // Taking advantage of the implicit constructor
         Player self;

         // Initializing all the members
         self.name = name;
         self.position[0] = x;
         self.position[1] = y;

         // Returning the reference of the object
         return self;
     }

     string toString()
     {
         return format("Hello i am '%s' and at the coordinate x%s / y%s",
             this.name, this.position[0], this.position[1]);
     }
}

void main()
{
     auto foo = Player("Foo", 2.7, 10.6);
     auto bar = Player();
     Player baz;

     writefln("%s\n%s\n%s", foo, bar, baz);
}

// == RDMD OUTPUT ==
// Entering the explicit constructor as 'Foo'
// Entering the explicit constructor as 'Bar'
// Hello i am 'Foo' and at the coordinate x2.7 / y10.6
// Hello i am 'Bar' and at the coordinate x1 / y1
// Hello i am 'Baz' and at the coordinate x0 / y0


You won't ever get the same support for this as C++. D is very clear 
that a struct must be constructable from its init value, and be valid.

For instance:

auto p = new Player[1];
assert(p[0].name == "Baz");

-Steve