if (int bar = .. bug or some thing

[Jonathan M Davis]

On Tuesday, October 31, 2017 04:08:12 Joel via Digitalmars-d-learn wrote:
> The following code assert fails (bar == 1, not -10!). I've wasted
> a bit of time because of this happening.
>
> void main() {
>   if (int bar = foo() != 0) {
>       assert(bar == -10);
>   }
> }
>
> auto foo() {
>   return -10;
> }

Why would you expect it to be -10? bar is assigned the result of foo() != 0,
which is a boolean result and will be either true or false. When that's
assigned to int, a conversion occurs, and that conversion treats true as 1
and false as 0. If you want the result to be -10, then you need to assign
the result of foo() to bar, not the result of foo() != 0. Now, because 0 is
treated as false, you could probably still do

if(int bar = foo())

rather than something like

int bar = foo();
if(bar != 0)

but regardless, the result of foo() != 0 is going to be bool, not int, so
all you'll ever get out of it is true or false, which will then be 1 or 0 if
converted to int.

- Jonathan M Davis