On Thursday, 30 December 2021 at 01:04:10 UTC, Ali Çehreli wrote:
The second item in the documentation mentions "any number of
default parameters" when describing copy constructor syntax:
https://dlang.org/spec/struct.html#struct-copy-constructor
1) I can't figure out how to use those extra parameters. For
example, I can't find a special function name to call
explicitly:
S.__cctor(a, 42); // No go
Behold the pathetic hack!
```d
import std.stdio:writeln;
struct A
{
this(ref return scope A rhs) inout {}
// copy constructor
this(ref A rhs, int b = 7) inout { // copy
constructor with default parameter
if (b != 7) {
rhs.b = b;//yes, modify the parameter, not the this
object :(
rhs.a = rhs.a;
}
else
foreach (i, ref field; rhs.tupleof)
field = this.tupleof[i] ;
}
this(this) @disable;
int a=4;
int b=3;
}
void main()
{
A a = A();
A b = void;
a.__ctor(b, 9); // because writing A b = A(a, 9); like a sane
human is giving errors D:
writeln(b.b);
}
```
Replacing `a.__ctor(b, 9);` with `A b = A(a, 9);` is yielding:
```d
onlineapp.d(26): Error: cannot implicitly convert expression `a`
of type `A` to `int`
```
