Hi,

I build some framework to access Delphi components from D.
Delphi supports property array access "StringGrid1.Columns[2]" which is translated in Delphi to a private method call "GetColumn(2)".

I need to imitate this behavior in my D code.
Therefore my TCustomGrid class has a inner struct ColumnsArray with an opIndex.
While accessing opIndex I need to call a DLL method. Therefore I need the "reference" attribute which is available in my TCustomGrid via inheritance.

To make my question short:) If ColumnsArray is a class I can access the attribute "reference" but not if it is a struct. I would rather prefer a struct, but with a struct
it seems I cannot access "reference".

How can I access "reference" from my inner struct?

class TCustomGrid: TCustomPresentedScrollBox
{	
	struct ColumnsArray
	{
		TColumn opIndex(int index)
		{
			int r = getIntegerIndexedPropertyReference(reference, "Columns", index);
			return new TColumn(r);
		}
	}
	
	ColumnsArray Columns;
...
}

Kind regards
André

On Monday, 28 August 2017 at 21:52:58 UTC, Andre Pany wrote:
> [...]
>
> To make my question short:) If ColumnsArray is a class I can access the attribute "reference" but not if it is a struct. I would rather prefer a struct, but with a struct
> it seems I cannot access "reference".
>
> How can I access "reference" from my inner struct?
>
> [...]

Add an explicit class reference member to to it:
---
class TCustomGrid: TCustomPresentedScrollBox
{
	struct ColumnsArray
	{
		TCustomGrid parent;

		TColumn opIndex(int index)
		{
			int r = getIntegerIndexedPropertyReference(reference, "Columns", index);
			return new TColumn(r);
		}
	}
	
	ColumnsArray Columns;

	this()
	{
		Columns = ColumnsArray(this);
	}
...
}
---

Nesting structs inside anything other than functions[1] is for visibility/protection encapsulation and namespacing only.

[1] non-static structs in functions are special as they have access to the surrounding stack frame

On Monday, 28 August 2017 at 22:28:18 UTC, Moritz Maxeiner wrote:
> On Monday, 28 August 2017 at 21:52:58 UTC, Andre Pany wrote:
>> [...]
>>
>> To make my question short:) If ColumnsArray is a class I can access the attribute "reference" but not if it is a struct. I would rather prefer a struct, but with a struct
>> it seems I cannot access "reference".
>>
>> How can I access "reference" from my inner struct?
>>
>> [...]
>
> Add an explicit class reference member to to it:
> ---
> class TCustomGrid: TCustomPresentedScrollBox
> {
> 	struct ColumnsArray
> 	{
> 		TCustomGrid parent;
>
> 		TColumn opIndex(int index)
> 		{
> 			int r = getIntegerIndexedPropertyReference(reference, "Columns", index);
> 			return new TColumn(r);
> 		}
> 	}
> 	
> 	ColumnsArray Columns;
>
> 	this()
> 	{
> 		Columns = ColumnsArray(this);
> 	}
> ...
> }
> ---
>
> Nesting structs inside anything other than functions[1] is for visibility/protection encapsulation and namespacing only.
>
> [1] non-static structs in functions are special as they have access to the surrounding stack frame

Unfortunately thats not possible. ColumnsArray and the attribute will become a string mixin to avoid boilerplate.

It would be error prone if I have to initialize them in the constructor too. I want just 1 single coding line for this property. That is also the reason I do not want to use a class, as I would have to initialize them in the constructor.

Kind regards
André

On Monday, 28 August 2017 at 22:47:12 UTC, Andre Pany wrote:
> On Monday, 28 August 2017 at 22:28:18 UTC, Moritz Maxeiner wrote:
>> On Monday, 28 August 2017 at 21:52:58 UTC, Andre Pany wrote:
>>> [...]
>>>
>>> To make my question short:) If ColumnsArray is a class I can access the attribute "reference" but not if it is a struct. I would rather prefer a struct, but with a struct
>>> it seems I cannot access "reference".
>>>
>>> How can I access "reference" from my inner struct?
>>>
>>> [...]
>>
>> Add an explicit class reference member to to it:
>> ---
>> class TCustomGrid: TCustomPresentedScrollBox
>> {
>> 	struct ColumnsArray
>> 	{
>> 		TCustomGrid parent;
>>
>> 		TColumn opIndex(int index)
>> 		{
>> 			int r = getIntegerIndexedPropertyReference(reference, "Columns", index);
>> 			return new TColumn(r);
>> 		}
>> 	}
>> 	
>> 	ColumnsArray Columns;
>>
>> 	this()
>> 	{
>> 		Columns = ColumnsArray(this);
>> 	}
>> ...
>> }
>> ---
>>
>> Nesting structs inside anything other than functions[1] is for visibility/protection encapsulation and namespacing only.
>>
>> [1] non-static structs in functions are special as they have access to the surrounding stack frame
>
> Unfortunately thats not possible. ColumnsArray and the attribute will become a string mixin to avoid boilerplate.
>
> It would be error prone if I have to initialize them in the constructor too. I want just 1 single coding line for this property. That is also the reason I do not want to use a class, as I would have to initialize them in the constructor.

---
class C
{
    struct S
    {
    }
    S s;
}
---

is semantically equivalent to

---
struct S
{
}

class C
{
    S s;
}
---

with the two differences being
- namespacing (outside of C one has to use C.S to access S)
- you can protect the visibility of the S from outside the module C resides in via private,public, etc.

In both cases S doesn't inherently how about C, which means a solution using default initialization is not feasible, as S.init can't know about any particular instance of C.
I don't think there's any way for you to avoid using a class constructor.

On Monday, 28 August 2017 at 23:12:40 UTC, Moritz Maxeiner wrote:
>
> In both cases S doesn't inherently how about C, which means a solution using default initialization is not feasible, as S.init can't know about any particular instance of C.
> I don't think there's any way for you to avoid using a class constructor.

Thanks for the explanation. I now tried to use a class and use a static opIndex. But it seems from a static method you also cannot access the attributes of a outer class :)

class TCustomGrid: TCustomPresentedScrollBox
{	
	class ColumnsArray
	{
		static TColumn opIndex(int index)
		{
			// Reference is defined in TCustomGrid via inheritene
			int r = getIntegerIndexedPropertyReference(reference, "Columns", index);
			return new TColumn(r);
		}
	}
	
	alias Columns = ColumnsArray;
...
}

This seems like an unnecessary limitation...

Kind regards
André

On Tuesday, 29 August 2017 at 07:59:40 UTC, Andre Pany wrote:
> On Monday, 28 August 2017 at 23:12:40 UTC, Moritz Maxeiner wrote:
>>
>> In both cases S doesn't inherently how about C, which means a solution using default initialization is not feasible, as S.init can't know about any particular instance of C.
>> I don't think there's any way for you to avoid using a class constructor.
>
> Thanks for the explanation. I now tried to use a class and use a static opIndex. But it seems from a static method you also cannot access the attributes of a outer class :)

A nested class' outer property (when nested inside another class) is a class reference, which means we not only require a class instance of the outer class to reference, but also a class instance of the nested class to store said class reference to the other class in.
A static class method (by definition) is invoked without a class instance.
The two are inherently incompatible.

> [...]
>
> This seems like an unnecessary limitation...

I can only recommend reading the language specification w.r.t, nested classes [1] if it seems that way to you, because it is not.

[1] https://dlang.org/spec/class.html#nested

On Tuesday, 29 August 2017 at 08:30:24 UTC, Moritz Maxeiner wrote:
> On Tuesday, 29 August 2017 at 07:59:40 UTC, Andre Pany wrote:
>> On Monday, 28 August 2017 at 23:12:40 UTC, Moritz Maxeiner wrote:
>>>
>>> In both cases S doesn't inherently how about C, which means a solution using default initialization is not feasible, as S.init can't know about any particular instance of C.
>>> I don't think there's any way for you to avoid using a class constructor.
>>
>> Thanks for the explanation. I now tried to use a class and use a static opIndex. But it seems from a static method you also cannot access the attributes of a outer class :)
>
> A nested class' outer property (when nested inside another class) is a class reference, which means we not only require a class instance of the outer class to reference, but also a class instance of the nested class to store said class reference to the other class in.
> A static class method (by definition) is invoked without a class instance.
> The two are inherently incompatible.
>
>> [...]
>>
>> This seems like an unnecessary limitation...
>
> I can only recommend reading the language specification w.r.t, nested classes [1] if it seems that way to you, because it is not.
>
> [1] https://dlang.org/spec/class.html#nested

I think I found a solution which fulfills all goals but I have to try it out. A property method "Columns" will return an initialized struct "ColumnsArray" as proposed by you.
This should nicely work as string mixin. Thanks for your help.

Kind regards
André