Re: Accessing outer class attribute from inner struct
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
Re: Accessing outer class attribute from inner struct
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
Re: Accessing outer class attribute from inner struct
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
Re: Accessing outer class attribute from inner struct
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.
Re: Accessing outer class attribute from inner struct
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
Re: Accessing outer class attribute from inner struct
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
Accessing outer class attribute from inner struct
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
