I have used alias this and found odd behaviour in complex code.

I tracked the problem down and was able to replicate it with a much simpler case as given below.

I'm new to D (but have read TDPL).
Is this my mis-understanding or a defect?

Many thanks, Kieron

----- self contained d sample starts -----
import std.stdio, std.math;

void main()
{
    auto p = Test(0.5, 0.5);
    assert(0.5 == p.a); // ok
    assert(0.5 == p.b); // ok
    Test q;
//  q = Test(0.5, 0.5);
    //
    // the above line gave same
    // error when subst for
    // the line below
    q = p;
    if (isNaN(q.b))
        printf("problem replicated\n");
    assert(0.5 == q.a); // ok
    assert(0.5 == q.b); // this fails
}

struct Test
{
    double a;
    double b;
    alias a this;
}
----- end of file -----

On Mon, 30 Aug 2010 13:12:00 -0400, Kieron Brown <kieron_brown@hotmail.com> wrote:

> I have used alias this and found odd behaviour in complex code.
>
> I tracked the problem down and was able to replicate it
> with a much simpler case as given below.
>
> I'm new to D (but have read TDPL).
> Is this my mis-understanding or a defect?
>
> Many thanks, Kieron
>
> ----- self contained d sample starts -----
> import std.stdio, std.math;
>
> void main()
> {
>     auto p = Test(0.5, 0.5);
>     assert(0.5 == p.a); // ok
>     assert(0.5 == p.b); // ok
>     Test q;
> //  q = Test(0.5, 0.5);
>     //
>     // the above line gave same
>     // error when subst for
>     // the line below
>     q = p;
>     if (isNaN(q.b))
>         printf("problem replicated\n");
>     assert(0.5 == q.a); // ok
>     assert(0.5 == q.b); // this fails
> }
>
> struct Test
> {
>     double a;
>     double b;
>     alias a this;
> }

Yes, that's a bug.

-Steve