Small suggestion for default constructors

[Ali Çehreli]

On 1/16/23 19:12, Adam D Ruppe wrote:
 >          // one little function
 >          this(typeof(this.tupleof) t) {
 >                  this.tupleof = t;
 >          }

Which can be mixed-in and can have default arguments:

mixin template memberAssigningConstructor() {
     // one little function
     this(typeof(this.tupleof) t = typeof(this.tupleof).init) {
         this.tupleof = t;
     }
}

import std.stdio;

class Foo {
     int x;
     int y;
     int z;

     mixin memberAssigningConstructor!();

     override string toString() const {
         import std.format : format;
         return format!"%s %s %s"(x, y, z);
     }
}

void testWith(Args...)(Args args) {
     auto f = new Foo(args);
     writeln(f);
}

void main() {
     testWith();
     testWith(1);
     testWith(1, 2);
     testWith(1, 2, 3);
}

Outputs:

0 0 0
1 0 0
1 2 0
1 2 3

However, I recommend testing compilation speeds because I used mixed-in 
tupleof for opCmp implementations in a project about 3 years ago. There 
were only 6 instances of that usage but the compilation times were 
noticeably affected. (Disclaimer: There were 6 instances but I think 
those modules were imported very many times by other modules.)

Replacing the tupleof idiom with trivial functions fixed the compilation 
speed issue for me.

Ali