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digitalmars.D.learn - [question] Access from UDA constructor to parent symbol

reply crimaniak <crimaniak gmail.com> writes:
```
class uda
{
     this()
     {
          // I want to see Foo here and use it's reflection to 
iterate fields and methods.
     }
}


 uda
struct Foo
{

}

```
Is there a way to do it?
Dec 26 2016
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Monday, 26 December 2016 at 20:07:56 UTC, crimaniak wrote:

          // I want to see Foo here and use it's reflection to 
 iterate fields and methods.


then pass foo to it....

What do you mean parent symbol? I assumed you mean subclass but 
your example shows one class and one struct. So is it the 
structure containing the class? Or what?


But, the answer of just passing the argument is probably the best 
one anyway. You can use a factory function, or pass the type from 
a constructor to a super method, or something like that.
Dec 26 2016
next sibling parent reply crimaniak <crimaniak gmail.com> writes:
On Monday, 26 December 2016 at 21:15:03 UTC, Adam D. Ruppe wrote:

 On Monday, 26 December 2016 at 20:07:56 UTC, crimaniak wrote:

          // I want to see Foo here and use it's reflection to 
 iterate fields and methods.


 then pass foo to it....

 What do you mean parent symbol? I assumed you mean subclass but 
 your example shows one class and one struct. So is it the 
 structure containing the class? Or what?


I mean the character to which the attribute belongs, Foo in this 
case.


 But, the answer of just passing the argument is probably the 
 best one anyway. You can use a factory function, or pass the 
 type from a constructor to a super method, or something like 
 that.


Let me explain. I want to have struct Foo : BarInterface {}. I 
read forums and found some discussion. Arguments against this 
feature has no sense on my opinion. But in fact I don't think it 
will be implemented. So I try to implement it as library. My idea:

class implements(Interface)
{
	this()
	{
		// iterate all members of Interface and check if this element
		// exists in parent symbol and check if parameters the same.
		// Write clean error message if contract fails.
	}
}

unittest
{
	interface I1
	{
		void foo();
		int bar(int i);
	}


	 implements!I1
	struct S1
	{
		void foo()
		{
			import std.stdio;
			writeln("foo");
		}

		// I want error message like "function int bar(int i) should be 
implemented according to interface I1" in this case
	}
}

So, if I pass both types in parameters it will not be so clean. 
It will be some separate from struct expression, but I want 
attribute like above.

It seems I can find symbol iterating all symbols in __MODULE__but 
in this case it will be O(N^2), there N is amount of  implements 
usages in module.

I also thought about such option:

struct S1
{
	mixin implements!I1;
	...
}

But this option I like less, and I have not researched it.

So my main question: how it is possible to do such thing?
Dec 26 2016
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 12/26/2016 02:04 PM, crimaniak wrote:


 So my main question: how it is possible to do such thing?


Just to make sure we're on the same page: :)

* There is 'interface' in addition to 'class'

* If all you want is to check, then you can write template constraints 
by following the example of std.range.isInputRange.

With that aside, what you need is generally achieved by a mixin:

 implements!I1
struct S1
{
     // ...
}

template ValidateInterfaces() {
     // Go through all members of the module here
     // Identify the ones having the 'implements' UDA
     // The useful tools here are
     //     __traits(getAttributes)
     //     __traits(allMembers)
     //     __traits(getMember)
}

mixin ValidateInterfaces;

Ali
Dec 26 2016
parent crimaniak <crimaniak gmail.com> writes:
On Tuesday, 27 December 2016 at 02:05:27 UTC, Ali Çehreli wrote:

 On 12/26/2016 02:04 PM, crimaniak wrote:


 So my main question: how it is possible to do such thing?


 Just to make sure we're on the same page: :)

 * There is 'interface' in addition to 'class'


  Yes. I want it for structs exactly.

 * If all you want is to check, then you can write template 
 constraints by following the example of std.range.isInputRange.


  Interface implementation has a significant advantage over 
template constraints for implementation break case. With 
interface I have one relevant error on the implementation stage. 
With template constraints I have many less relevant errors on the 
usage stage. It's just different types of contract.


 With that aside, what you need is generally achieved by a mixin:

  implements!I1
 struct S1
 {
     // ...
 }

 template ValidateInterfaces() {
     // Go through all members of the module here
     // Identify the ones having the 'implements' UDA
     // The useful tools here are
     //     __traits(getAttributes)
     //     __traits(allMembers)
     //     __traits(getMember)
 }

 mixin ValidateInterfaces;


Thanks, this is a way. The only problem user can forget to call 
this mixin. It would be useful to have module-wide compile-time 
variables, in this case it's possible to call ValidateInterfaces 
one time from first  implements instance and user don't have to 
write it at every module.
Dec 27 2016
prev sibling parent Jerry <hurricane hereiam.com> writes:
On Monday, 26 December 2016 at 21:15:03 UTC, Adam D. Ruppe wrote:

 On Monday, 26 December 2016 at 20:07:56 UTC, crimaniak wrote:

          // I want to see Foo here and use it's reflection to 
 iterate fields and methods.


 then pass foo to it....

 What do you mean parent symbol? I assumed you mean subclass but 
 your example shows one class and one struct. So is it the 
 structure containing the class? Or what?


 But, the answer of just passing the argument is probably the 
 best one anyway. You can use a factory function, or pass the 
 type from a constructor to a super method, or something like 
 that.


I think he wants the symbol that the UDA is attached to.

So instead of doing:

struct attribN(I, T) { }

 attrib1!(Implement1, MyStructName)
 attrib2!(Implement2, MyStructName)
struct MyStructName
{
}


you could instead possibly add a feature to do this:

struct attribN(I, T = __UDA__)
{
}

// or possibly

class attribN(I) : Attribute // Attribute then contains the 
symbol its connected to
{
}


 attrib1!Implement1
 attrib2!Implement2
struct MyStructName
{
}

Not likely a feature to be added though.
Dec 27 2016