Hello,

Cannot find corresponding opSomething method, if any. (opDispatch seems to specialise for method call.)
Else, how to catch obj.member?

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

spir <denis.spir@gmail.com> wrote:

> Hello,
>
> Cannot find corresponding opSomething method, if any. (opDispatch seems to specialise for method call.)
> Else, how to catch obj.member?

opDispatch is likely what you want. with the @property annotation, it
will readily support obj.member; and obj.member = foo; syntax.

-- 
Simen

On 01/25/2011 10:29 PM, Simen kjaeraas wrote:
> spir <denis.spir@gmail.com> wrote:
>
>> Hello,
>>
>> Cannot find corresponding opSomething method, if any. (opDispatch seems to
>> specialise for method call.)
>> Else, how to catch obj.member?
>
> opDispatch is likely what you want. with the @property annotation, it
> will readily support obj.member; and obj.member = foo; syntax.

Thank you, Simen, i'll try using opDispatch with @property. But I'm not sure how to write that concretely. My use case is of a type holding a string[AnyThing] AA called symbols. Then, I wish to map
	obj.id
to
	obj.symbols["id"]
(hope I'm clear)

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

spir <denis.spir@gmail.com> wrote:

> On 01/25/2011 10:29 PM, Simen kjaeraas wrote:
>> spir <denis.spir@gmail.com> wrote:
>>
>>> Hello,
>>>
>>> Cannot find corresponding opSomething method, if any. (opDispatch seems to
>>> specialise for method call.)
>>> Else, how to catch obj.member?
>>
>> opDispatch is likely what you want. with the @property annotation, it
>> will readily support obj.member; and obj.member = foo; syntax.
>
> Thank you, Simen, i'll try using opDispatch with @property. But I'm not sure how to write that concretely. My use case is of a type holding a string[AnyThing] AA called symbols. Then, I wish to map
> 	obj.id
> to
> 	obj.symbols["id"]
> (hope I'm clear)

I just found that it is, in fact, unpossible. That is, you can support
either a = foo.id; or foo.id = a; - not both. This is caused by bug 620:
http://d.puremagic.com/issues/show_bug.cgi?id=620

-- 
Simen

On 01/26/2011 12:05 AM, spir wrote:
> On 01/25/2011 10:29 PM, Simen kjaeraas wrote:
>> spir <denis.spir@gmail.com> wrote:
>>
>>> Hello,
>>>
>>> Cannot find corresponding opSomething method, if any. (opDispatch seems to
>>> specialise for method call.)
>>> Else, how to catch obj.member?
>>
>> opDispatch is likely what you want. with the @property annotation, it
>> will readily support obj.member; and obj.member = foo; syntax.
>
> Thank you, Simen, i'll try using opDispatch with @property. But I'm not sure
> how to write that concretely. My use case is of a type holding a
> string[AnyThing] AA called symbols. Then, I wish to map
> obj.id
> to
> obj.symbols["id"]
> (hope I'm clear)
>
> Denis

Right, just understood that you meant, I guess: since D supports properties with "x.a" syntax mapping to a func call x.a() under the hood, then one can use opDispatch intended for func calls to dispatch plain data membar access. (woof!).
FWIW: the following works fine:

alias int[string] Symbols;

class T {
    int i;
    Symbols symbols;
    this (int i, Symbols symbols) {
        this.i = i;
        this.symbols = symbols;
    }
    auto opDispatch (string name) () {
        auto p = (name in this.symbols);
        if (p)
            return *p;
        throw new Exception("No symbol called "~name~".");
    }
}
unittest {
    auto t = new T(1, ["j":2, "k":3]);
    writeln(t.i);
    writeln(t.j);
    writeln(t.k);
    writeln(t.l);   // throws as expected
}


Denis
-- 
_________________
vita es estrany
spir.wikidot.com

On 01/26/2011 01:06 AM, Simen kjaeraas wrote:
> spir <denis.spir@gmail.com> wrote:
>
>> On 01/25/2011 10:29 PM, Simen kjaeraas wrote:
>>> spir <denis.spir@gmail.com> wrote:
>>>
>>>> Hello,
>>>>
>>>> Cannot find corresponding opSomething method, if any. (opDispatch seems to
>>>> specialise for method call.)
>>>> Else, how to catch obj.member?
>>>
>>> opDispatch is likely what you want. with the @property annotation, it
>>> will readily support obj.member; and obj.member = foo; syntax.
>>
>> Thank you, Simen, i'll try using opDispatch with @property. But I'm not sure
>> how to write that concretely. My use case is of a type holding a
>> string[AnyThing] AA called symbols. Then, I wish to map
>> obj.id
>> to
>> obj.symbols["id"]
>> (hope I'm clear)
>
> I just found that it is, in fact, unpossible. That is, you can support
> either a = foo.id; or foo.id = a; - not both. This is caused by bug 620:
> http://d.puremagic.com/issues/show_bug.cgi?id=620

I do not really understand the subtleties of this bug, but indeed, I found no way to use opDispatch to set data members.
In other words, I could implement python's __getattr__ or Lua's __index,
not  python's __setattr__ or Lua's __newindex.

EDIT: Could do this as a workaround.

alias int[string] Symbols;

class T {
    int i;
    Symbols symbols;
    this (int i, Symbols symbols) {
        this.i = i;
        this.symbols = symbols;
    }
    auto opDispatch (string name) () {
        writeln("get");
        auto p = (name in this.symbols);
        if (p)
            return *p;
        throw new Exception("No symbol called "~name~".");
    }
    auto opDispatch (string name, Value) (Value value) {
        writeln("set ");
        auto p = (name in this.symbols);
        if (p) {
            *p = value;
            return;
        }
        throw new Exception("No symbol called '"~name~"'.");
    }
}
unittest {
    auto t = new T(1, ["j":2, "k":3]);
    writefln("<%s %s %s>", t.i, t.j,t.k);
    t.i = 11;
    t.j(22);
    t.k(33);
    writefln("<%s %s %s>", t.i, t.j,t.k);
//~     writeln(t.l);   // throws as expected
//~     t.l(44);   // throws as expected
    t.j = 222;  // Error: function
                // __trials__.T.opDispatch!("j").opDispatch ()
                // is not callable using argument types (int)
}

The last example shows how normal member-set syntax fails. I would like to know into what
	obj.name = val
is rewritten.

Denis
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