Functional tools for D

[Daniel Keep]

map should now be fixed to return the actual type, and I've uploaded the
file to Wiki4D.  I actually couldn't find the source for this, so when I
downloaded it off the DM news archive (Thunderbird doesn't have my
original message :P) I had to go rebuild all the indenting.  Fun, fun, fun!

http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/functools

Your original example should look like this:

    auto ids = map(persons, (Person p) { return p.id; });

Have fun, and hope it's all actually working this time :P

	-- Daniel

Daniel Keep wrote:
> 
> Vassily Gavrilyak wrote:
>> Cool stuff, almost what I searched for. filter works like a charm.
>> However not so for map and reduce. The return type of map and reduce is different
>> from the type of item in collection.
>> I'm just started to look at D, so don't know the right way to write those functions.
>> Declaration in Nemerle looks like this
>> public Map['a, 'b] (l : list ['a], f : 'a -> 'b) : list ['b] {
>>       $[ f(x) | x in l ]
>> }
>> So we have 2 types here, type of collection and type of result
>> And reduce(fold) has 2 types too.
>> So basically the following code:
>>
>> struct Person{   int id;  char[] name;}
>> static Person[] people= [{1, "Joe"}, {2, "Bill"}];
>> int[] ids = map(persons, delegate int(Person p){return p.id;});
>>
>> should produce [1,2]
>>
>> Is that possible in D?
> 
> Wow; it's been a while :P  I think this is the first reply I got to that
> post.
> 
> Having a quick squizz at the code; you're right.  The way I've derived
> the return type of map is completely wrong.  I'll put that on my list of
> things to fix :P
> 
> So in answer to your question, yes it should be entirely possible.  The
> trick, in this case, is the following:
> 
>   static if( is( tOp tReturnType == return ) )
> 
> Which will derive the return type of the function.
> 
>   -- Daniel
> 
> Incidentally, Nemerle is looking less and less like C# every time I see
> it :P
> 

-- 
Unlike Knuth, I have neither proven or tried the above; it may not even
make sense.

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