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digitalmars.D.learn - compile time class introspection?

reply serg <why.you.need my.email> writes:
Is there any way to find out if a template parameter has method?

I was naively hoped for tupleof to help, but it seems not =(

-- serg.
Jun 14 2007
parent reply serg <why.you.need my.email> writes:
What really want is, to have a template mixin method that depending on class it
inserted into, could call internally a member method if it available.

Something like this:

template dispatchT(T)
{
    void dispatch(int msg)
    {
        switch (msg)
        {
        case WM_CLOSE:
            static if (OnClose in T) // <-- T has desired method
                return OnClose();
            static else
                break;
        case WM_DESTROY:
            static if (T.OnDestroy) // <-- same, but different syntax
                return OnDestroy();
            static else
                break;
        default:
        }
        return DefWndProc();
    }
}

class Window
{
    void OnClose(){}
    void OnDestroy(){}
    mixin dispatchT!(Window);
}


-- serg.
Jun 14 2007
next sibling parent Daniel Keep <daniel.keep.lists gmail.com> writes:
class A { void foo() {} }
class B { void bar() {} }

A a;
B b;

assert( is( typeof(&a.foo) ) );
assert( is( typeof(&b.bar) ) );
assert(!is( typeof(&a.bar) ) );
assert(!is( typeof(&b.foo) ) );

Or something like that.

	-- Daniel
Jun 14 2007
prev sibling parent reply Max Samukha <samukha voliacable.com.removethis> writes:
On Thu, 14 Jun 2007 09:27:50 -0400, serg <why.you.need my.email>
wrote:


What really want is, to have a template mixin method that depending on class it
inserted into, could call internally a member method if it available.

Something like this:

template dispatchT(T)
{
    void dispatch(int msg)
    {
        switch (msg)
        {
        case WM_CLOSE:
            static if (OnClose in T) // <-- T has desired method
                return OnClose();
            static else
                break;
        case WM_DESTROY:
            static if (T.OnDestroy) // <-- same, but different syntax
                return OnDestroy();
            static else
                break;
        default:
        }
        return DefWndProc();
    }
}

class Window
{
    void OnClose(){}
    void OnDestroy(){}
    mixin dispatchT!(Window);
}


-- serg.


You might do it like this:

template dispatchT(T)
{
    void dispatch(int msg)
    {
        switch (msg)
        {
            static if (is(typeof(T.OnClose)))
            {
                case WM_CLOSE:
                    return T.OnClose();                    
            }
            else static if (is(typeof(T.OnDestroy)))
            {
                case WM_DESTROY:
                    return T.OnDestroy();                  
            }
        default:
	
        }
    }
}
Jun 14 2007
parent reply serg <why.you.need my.email> writes:
Max Samukha Wrote:

 You might do it like this:
 ...
             static if (is(typeof(T.OnClose)))
 ...


Yes, this is exactly what I was looked for!

Thanks, Max!

-- serg.
Jun 14 2007
parent reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
serg wrote:

 Max Samukha Wrote:

 You might do it like this:
 ...
             static if (is(typeof(T.OnClose)))
 ...


 
 Yes, this is exactly what I was looked for!
 
 Thanks, Max!
 
 -- serg.


This is an important thing about D that probably deserves a long and 
extensive tutorial somewhere...  Many of its cooler features aren't 
really features at all, but side-effects of other more general features. 
  So, to reuse this same example, no D doesn't have a way to ask if a 
class or structure has a particular method.  D /does/ have a way to 
check for valid types... which, incidentally, non-existant members are 
invalid types.  So, voila, a side-effect of checking its type is that 
you confirm it exists.

There are others... a plethora, even.  Walter is fond of lots of small 
things that can be put together to achieve amazing things -- and I don't 
strictly disagree -- but it isn't usually obvious what you can do with 
those nifty little gadgets.

-- Chris Nicholson-Sauls
Jun 14 2007
parent reply Serg Kovrov <kovrov bugmenot.com> writes:
Chris Nicholson-Sauls wrote:

 This is an important thing about D that probably deserves a long and 
 extensive tutorial somewhere...  Many of its cooler features aren't 
 really features at all, but side-effects of other more general features. 


I hope it won't happen. Let me explain..

Considered to be a side-effect (or hack), this rather should be 
redesigned than teaching in docs/tutorials/books. That way we end up 
with yet another C++

Its sad that I actually will use this hack (that is, will produce code 
I'm not proud with). I can't just hope and wait for this to be fixed 
(properly designed), as temptation to have this functionality is to strong.


PS. Don't get me wrong, I really do like D
-- serg.
Jun 14 2007
parent reply janderson <askme me.com> writes:
Serg Kovrov wrote:

 Chris Nicholson-Sauls wrote:

 This is an important thing about D that probably deserves a long and 
 extensive tutorial somewhere...  Many of its cooler features aren't 
 really features at all, but side-effects of other more general features. 


 
 I hope it won't happen. Let me explain..
 
 Considered to be a side-effect (or hack), this rather should be 
 redesigned than teaching in docs/tutorials/books. That way we end up 
 with yet another C++
 
 Its sad that I actually will use this hack (that is, will produce code 
 I'm not proud with). I can't just hope and wait for this to be fixed 
 (properly designed), as temptation to have this functionality is to strong.
 
 
 PS. Don't get me wrong, I really do like D
 -- serg.


I disagree, I think an orthogonal design like D is a good thing in many 
cases.  It means that you don't have to learn so many keywords and are 
more likely to determine the syntax yourself.  It also means code is 
generally easier to maintain due to generalization because you can often 
   reuse the code in more different ways then originally intended.

I don't regard the solution given as a hack it seems pretty obvious to 
me.  Either way it would have to be documented.  If you don't like it, 
write a wrapper template.

Also I don't think good orthogonality means the language has to get more 
complex.  I think its about making the common coding primitives easy to 
use however also making them powerful enough if the user wants to extend 
them to something that is less common.

-Joel
Jun 14 2007
parent reply Serg Kovrov <kovrov bugmenot.com> writes:
janderson wrote:

 I disagree, I think an orthogonal design like D is a good thing in many 
 cases.  It means that you don't have to learn so many keywords and are 
 more likely to determine the syntax yourself.  It also means code is 
 generally easier to maintain due to generalization because you can often 
   reuse the code in more different ways then originally intended.
 
 I don't regard the solution given as a hack it seems pretty obvious to 
 me.  Either way it would have to be documented.  If you don't like it, 
 write a wrapper template.
 
 Also I don't think good orthogonality means the language has to get more 
 complex.  I think its about making the common coding primitives easy to 
 use however also making them powerful enough if the user wants to extend 
 them to something that is less common.
 
 -Joel


I'm not sure I understand what you mean by "orthogonal design", and what 
it has to do with code reuse? I was talking about language facilities, 
something not available as user or library code.

I just want to say I like idea of language features to be thoughtfully 
designed, as opposite to accidentally discovered side-effects. I have to 
say I don't really care about actual origin of a feature, but rather 
what it feels like.

-- serg.
Jun 15 2007
next sibling parent reply Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
Serg Kovrov wrote:

 janderson wrote:

 I disagree, I think an orthogonal design like D is a good thing in 
 many cases.  It means that you don't have to learn so many keywords 
 and are more likely to determine the syntax yourself.  It also means 
 code is generally easier to maintain due to generalization because you 
 can often   reuse the code in more different ways then originally 
 intended.

 I don't regard the solution given as a hack it seems pretty obvious to 
 me.  Either way it would have to be documented.  If you don't like it, 
 write a wrapper template.

 Also I don't think good orthogonality means the language has to get 
 more complex.  I think its about making the common coding primitives 
 easy to use however also making them powerful enough if the user wants 
 to extend them to something that is less common.

 -Joel


 
 I'm not sure I understand what you mean by "orthogonal design", and what 
 it has to do with code reuse? I was talking about language facilities, 
 something not available as user or library code.
 
 I just want to say I like idea of language features to be thoughtfully 
 designed, as opposite to accidentally discovered side-effects. I have to 
 say I don't really care about actual origin of a feature, but rather 
 what it feels like.
 
 -- serg.


I'm not positive that the side-effect in this case at least was 
accidental.  I seem to recall it was specifically made sure to work in 
the development of is() expressions.  (Could be wrong, it might've been 
talked about later.)  That said, I do hear you, and actually personally 
wish reflection capabilities had their own access point of some kind. 
I'd even live with a new keyword to activate that access -- in my 
opinion it'd be worth it.

Maybe a typeinfo() primitive alongside typeof() and typeid()... although 
that might be misleading since the objects returned by typeid() are 
descendants of the class TypeInfo; heh.

Or maybe just the obvious reflect(), which would return an object like 
typeid() does, but a TypeView or TypeInspect or somesuch.  Then provide 
reflection capabilities by way of that special class.

In respect to that, maybe there should be an equivelant 'reflected' or 
'reflect' (note the missing parentheses) attribute for marking a class 
as available for reflection.  That way we only include the extra 
information in cases where its deemed useful...

And now I'm at the point where I really should have started a new 
thread.  So I'll shut up now.  :)

-- Chris Nicholson-Sauls
Jun 15 2007
parent Christopher Wright <dhasenan gmail.com> writes:
Chris Nicholson-Sauls wrote:

 Serg Kovrov wrote:

 janderson wrote:

 I disagree, I think an orthogonal design like D is a good thing in 
 many cases.  It means that you don't have to learn so many keywords 
 and are more likely to determine the syntax yourself.  It also means 
 code is generally easier to maintain due to generalization because 
 you can often   reuse the code in more different ways then originally 
 intended.

 I don't regard the solution given as a hack it seems pretty obvious 
 to me.  Either way it would have to be documented.  If you don't like 
 it, write a wrapper template.

 Also I don't think good orthogonality means the language has to get 
 more complex.  I think its about making the common coding primitives 
 easy to use however also making them powerful enough if the user 
 wants to extend them to something that is less common.

 -Joel


 I'm not sure I understand what you mean by "orthogonal design", and 
 what it has to do with code reuse? I was talking about language 
 facilities, something not available as user or library code.

 I just want to say I like idea of language features to be thoughtfully 
 designed, as opposite to accidentally discovered side-effects. I have 
 to say I don't really care about actual origin of a feature, but 
 rather what it feels like.

 -- serg.


 
 I'm not positive that the side-effect in this case at least was 
 accidental.  I seem to recall it was specifically made sure to work in 
 the development of is() expressions.  (Could be wrong, it might've been 
 talked about later.)  That said, I do hear you, and actually personally 
 wish reflection capabilities had their own access point of some kind. 
 I'd even live with a new keyword to activate that access -- in my 
 opinion it'd be worth it.
 
 Maybe a typeinfo() primitive alongside typeof() and typeid()... although 
 that might be misleading since the objects returned by typeid() are 
 descendants of the class TypeInfo; heh.
 
 Or maybe just the obvious reflect(), which would return an object like 
 typeid() does, but a TypeView or TypeInspect or somesuch.  Then provide 
 reflection capabilities by way of that special class.
 
 In respect to that, maybe there should be an equivelant 'reflected' or 
 'reflect' (note the missing parentheses) attribute for marking a class 
 as available for reflection.  That way we only include the extra 
 information in cases where its deemed useful...
 
 And now I'm at the point where I really should have started a new 
 thread.  So I'll shut up now.  :)


Why not just improve .classinfo and apply it to structs as well? You'd 
want to rename it, probably...but if vtbl were an associative array of 
functioninfo[char[]] instead of a void*[], with a functioninfo 
definition including:
  - argument type tuple / array
  - return type
  - protection
  - static / nonstatic
  - pointer to classinfo, or null if it's a free function
  - pointer to the function

Overload opAssign so you can reassign functions at need, maybe, and then 
keep the pointer as read-only externally.

Do something similar with the members.

Of course flectioned does this. And flectioned is pretty much what the 
builtin reflection of D should hope to be.
Jun 15 2007
prev sibling parent janderson <askme me.com> writes:
Serg Kovrov wrote:

 janderson wrote:

 I disagree, I think an orthogonal design like D is a good thing in 
 many cases.  It means that you don't have to learn so many keywords 
 and are more likely to determine the syntax yourself.  It also means 
 code is generally easier to maintain due to generalization because you 
 can often   reuse the code in more different ways then originally 
 intended.

 I don't regard the solution given as a hack it seems pretty obvious to 
 me.  Either way it would have to be documented.  If you don't like it, 
 write a wrapper template.

 Also I don't think good orthogonality means the language has to get 
 more complex.  I think its about making the common coding primitives 
 easy to use however also making them powerful enough if the user wants 
 to extend them to something that is less common.

 -Joel


 
 I'm not sure I understand what you mean by "orthogonal design", and what 
 it has to do with code reuse? I was talking about language facilities, 
 something not available as user or library code.


Take the example of D's arrays.  They all work the same across the whole 
language.  One syntax applied across many different uses.  If you wish 
to change the type of the array, you don't have to change your interface 
to users, or search replace loads of code.  Furthermore, you don't have 
to write so many specialized templates.  That's what I mean by 
generalization resulting in more reusable code.


 
 I just want to say I like idea of language features to be thoughtfully 
 designed, as opposite to accidentally discovered side-effects. I have to 
 say I don't really care about actual origin of a feature, but rather 
 what it feels like.
 
 -- serg.


I think a good orthogonal language is thoughtfully designed and things 
aren't accidentally discovered, they are simply logically discovered. 
Its like lego, you can make a million things from it with good building 
blocks.

-Joel
Jun 15 2007