Hi,

I try to track down why some complex logic is not working. I think the root issue is that typeof() is not working in member methods. I reduced it to following example:

app.d(16): Error: this for Left needs to be type TBounds not type app.A
Failed: ["dmd", "-v", "-o-", "app.d", "-I."]

class TBounds
{
	@property float Left() {return 0.0;}
}

class A
{
	static void test()
	{
		typeof(TBounds.Left) m;
		
	}
	
	void test2()
	{
		typeof(TBounds.Left) m;
	}
}

void main() {}

How can I fix this issue?

Kind regards
André

On Wednesday, 26 July 2017 at 13:51:05 UTC, Andre Pany wrote:
> How can I fix this issue?

I would just do

       typeof((new TBounds).Left) m;


so then it is clear that you want a non-static member.

On Wednesday, 26 July 2017 at 14:05:12 UTC, Adam D. Ruppe wrote:
> On Wednesday, 26 July 2017 at 13:51:05 UTC, Andre Pany wrote:
>> How can I fix this issue?
>
> I would just do
>
>        typeof((new TBounds).Left) m;
>
>
> so then it is clear that you want a non-static member.

In my productive scenario I try to check whether a class (TLabel) has a specific member ("Margins.Left", "TextSettings.Font.Size").

mixin(`static if (!__traits(compiles, typeof(`~T.stringof~`.`~p.name~`))) {
...
}

This coding is within a member method and due to the issue with typeof it is failing.
Creating new class for checking whether the class has a specific member is not possible in my scenario, as a DLL call is involved and I need the result (member available) as condition for static if.

Due you think typeof should work within member methods and I should file an issue?

Kind regards
André

On Wednesday, 26 July 2017 at 16:50:35 UTC, Andre Pany wrote:
> mixin(`static if (!__traits(compiles, typeof(`~T.stringof~`.`~p.name~`))) {
> ...
> }

FYI, you shouldn't use .stringof here. Just use `T` instead of `T.stringof`.

> Creating new class for checking whether the class has a specific member is not possible in my scenario, as a DLL call is involved and I need the result (member available) as condition for static if.

This doesn't *actually* create a new class, it just compiles as if you would to make sure it has a valid `this` for it in the type system.

You could also use `typeof(TBounds.init.Left)`, which is actually even better than `new` since it doesn't require the constructor arguments.

But in either case, that code isn't actually run, it just looks for the non-static member function.

> Due you think typeof should work within member methods and I should file an issue?

I'm not sure... I could go either way on it since there is a reasonable answer here (int), but since it is non-static, trying to use it in an actual expression IS an error so it makes sense for typeof(error) to also be an error...

On Wednesday, 26 July 2017 at 17:04:59 UTC, Adam D. Ruppe wrote:
> On Wednesday, 26 July 2017 at 16:50:35 UTC, Andre Pany wrote:
>> [...]
>
> FYI, you shouldn't use .stringof here. Just use `T` instead of `T.stringof`.
>
> [...]

Thank you so much!

Kind regards
André

On Wednesday, 26 July 2017 at 19:06:24 UTC, Andre Pany wrote:
> On Wednesday, 26 July 2017 at 17:04:59 UTC, Adam D. Ruppe wrote:
>> On Wednesday, 26 July 2017 at 16:50:35 UTC, Andre Pany wrote:
>>> [...]
>>
>> FYI, you shouldn't use .stringof here. Just use `T` instead of `T.stringof`.
>>
>> [...]
>
> Thank you so much!
>
> Kind regards
> André

There's another method for such a check.

mixin(`static if (!is(typeof(T.`~p.name~`))))