On Friday, 25 May 2018 at 00:15:39 UTC, IntegratedDimensions
wrote:
On Thursday, 24 May 2018 at 23:31:50 UTC, Alex wrote:
On Thursday, 24 May 2018 at 20:24:32 UTC, IntegratedDimensions
wrote:
class T;
class TT : T;
interface I
{
@property T t();
}
abstract class A
{
T _t;
@property T t() { return _t; }
}
class C : A
{
// Stuff below uses t as TT but compiler, of course,
treats t as T
...
}
The issue is that I programmed the class C with a variable
that directly was based off TT, I later subderived T from TT
and exposed it in I. (TT was refactored in to T and not T)
As as a side note:
I can hardly follow this, as you don't show, where you use the
interface I. However, especially if TT was refactored in such
a way, that is a set difference of T and not T, why you choose
to derive from T instead of to contain T?
It really should be obvious that A was meant to derive from I.
This is just standard oop. Simply leaving off : I should not
be a deal breaker because it would not change the whole problem
from black to white or vice versa.
T is a member to be included. You can only derive from one
class. C can't derive from both A and T and even if it did, it
would mean something else.
https://en.wikipedia.org/wiki/Composition_over_inheritance
http://wiki.c2.com/?CompositionInsteadOfInheritance
Well, can imagine useful cases though...
This is not a composition pattern.
This is a parallel inherentence pattern.
TT : T = T
| | |
v v v
C : A : I
TT is used with C and T with I.
When C changes to C', TT : T changes to TT' : T
All functions that use TT in C are forced to use it as if it
were of type T rather than TT which requires a bunch of casts.
This is generally a violation of type logic. There is nothing
in that prevents t from being something like TTT which has no
direct relation to TT.
But the programming logic of the code enforces t to be of type
TT in C *always*. So I don't know why I would have to use
casting all the time. It would be nice if there where a simple
logical way to enforce a design pattern in the type system
knowing that it is enforced at runtime. This makes cleaner
code, nothing else.
But all the code in C assumes t is of type TT but now due to
the interface it looks like a T, even though internally it is
actually a TT.
What I'd like to do is
class C : A
{
private override @property TT t() { return cast(TT)(_t); }
// null check if necessary
// Stuff below uses t which is now a TT
...
}
or whatever.
This is simply so I don't have to rename or cast all my uses
of t in C to type TT.
I'm pretty much guaranteed that in C, t will be type TT due
to the design(C goes with TT like bread with butter).
So, it would be nice if somehow I could inform the type
system that in C, t is always of type TT and so treat it as
such rather than forcing me to explicitly cast for every use.
Again, I could rename things to avoid the same name usage but
in this case it is not necessary because of the design.
Is there any semantics that can get me around having to
rename?
Maybe, you are looking for Curiously Recurring Template
Pattern?
´´´
interface I(P)
{
@property P t();
}
abstract class T(P) : I!P
{
P _p;
@property P t() { return _p; }
}
class TT : T!TT
{
}
void main()
{
auto tt = new TT();
static assert(is(typeof(tt.t) == TT));
}
´´´
No, I am trying to keep parallel derived types consistently
connected. If A is derived from B and C from D and B uses D
then A uses C. Consistency cannot be guaranteed by the type
system at compile time because A is typed to use C, I want to
restrict it further to D.
You must put a template parameter in the interface and specialize
the class that implements the interface.
```
module runnable;
class T{}
class TT : T{}
interface I(N)
{
@property N t();
}
abstract class A(N) : I!N
{
N _t;
@property N t() { return _t; }
}
class C1 : A!T{}
class C2 : A!TT{}
void main(string[] args)
{
import std.traits;
static assert(is(ReturnType!(C1.t) == T));
static assert(is(ReturnType!(C2.t) == TT));
}
module runnable;
class T{}
class TT : T{}
interface I(N)
{
@property N t();
}
abstract class A(N) : I!N
{
N _t;
@property N t() { return _t; }
}
class C1 : A!T{}
class C2 : A!TT{}
void main(string[] args)
{
import std.traits;
static assert(is(ReturnType!(C1.t) == T));
static assert(is(ReturnType!(C2.t) == TT));
}
```
but obviously this won't work if you want to derive C1 or C2...
