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digitalmars.D.learn - Why can't typeof() be used in member method?

reply Andre Pany <andre s-e-a-p.de> writes:
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
Jul 26 2017
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
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.
Jul 26 2017
parent reply Andre Pany <andre s-e-a-p.de> writes:
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
Jul 26 2017
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
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...
Jul 26 2017
parent reply Andre Pany <andre s-e-a-p.de> writes:
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
Jul 26 2017
parent Temtaime <temtaime gmail.com> writes:
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~`))))
Jul 26 2017