dynamic classes and duck typing
Ary Borenszweig
ary at esperanto.org.ar
Tue Dec 1 04:05:16 PST 2009
Ary Borenszweig wrote:
> retard wrote:
>> Tue, 01 Dec 2009 03:16:47 -0800, Walter Bright wrote:
>>
>>> Ary Borenszweig wrote:
>>>> Can you show examples of points 2, 3 and 4?
>>> Have opDispatch look up the string in an associative array that returns
>>> an associated delegate, then call the delegate.
>>>
>>> The dynamic part will be loading up the associative array at run time.
>>
>> This is not exactly what everyone of us expected. I'd like to have
>> something like
>>
>> void foo(Object o) {
>> o.duckMethod();
>> }
>>
>> foo(new Object() { void duckMethod() {} });
>>
>> The feature isn't very dynamic since the dispatch rules are defined
>> statically. The only thing you can do is rewire the associative array
>> when forwarding statically precalculated dispatching.
>
> Exactly! That's the kind of example I was looking for, thanks.
Actuall, just the first part of the example:
void foo(Object o) {
o.duckMethod();
}
Can't do that because even if the real instance of Object has an
opDispatch method, it'll give a compile-time error because Object does
not defines duckMethod.
That's why this is something useful in scripting languages (or ruby,
python, etc.): if the method is not defined at runtime it's an error
unless you define the magic function that catches all. Can't do that in
D because the lookup is done at runtime.
Basically:
Dynanic d = ...;
d.something(1, 2, 3);
is just a shortcut for doing
d.opDispatch!("something")(1, 2, 3);
(and it's actually what the compiler does) but it's a standarized way of
doing that. What's the fun in that?
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