On Monday, 12 February 2018 at 03:13:43 UTC, aliak wrote:
Hi,
Is there a way to get post increment and pre increment working
properly in this scenario?
import std.stdio;
struct A {
int[] a;
this(int a) { this.a = [a]; }
auto opUnary(string op)(){
return A(mixin(op ~ "this.a[0]"));
}
}
void main() {
auto a = A(0);
int b = 0;
writeln(a++, ":", b++); // 1, 0 <-- wrong post increment
result
writeln(++a, ":", ++b); // 2, 2
}
writeln(a++) translates to:
A copy = a;
a.opUnary!"++";
writeln(copy);
copy.a[] and a.a[] are the same reference, you increment
a.a[0]/copy.a[0] in opUnary
to make this work you will need a postblit constructor:
struct A
{
....
this(this)
{
a = a.dup; //make a copy a;
}
}
In fact, you'll find exactly the same scenario in docs:
https://dlang.org/spec/struct.html#struct-postblit
If I switch the order of the mixin expression (i.e. "this.a[0]"
~ op) then the pre increment does not work.
Any tips?
Cheers
- Ali
