tdlp: higher-order functions

[Jerome BENOIT]

Hello Again:

On 20/01/12 15:58, Alex Rønne Petersen wrote:
> On 20-01-2012 15:32, Jerome BENOIT wrote:
>> Hello List:
>>
>> In tDlp book in section 5.6 entitled `Higher-Order Functions. Function
>> Literals,
>> the first code example is:
>>
>> -----------------------------------------------------------------
>> T[] find(alias pred, T)(T[] input)
>> if (is(typeof(pred(input[0])) == bool)) {
>> for(; input.length > 0; input = input[1 .. $]) {
>> if (pred(input[0])) break;
>> }
>> return input;
>> }
>> -----------------------------------------------------------------
>>
>> I can play it. Nevertheless, it is not clear for me right now
>> what is the role played by `T' in the generic argument list (alias pred,
>> T).
>> (Its meaning is bypassed in this section via a `deduction' way.)
>>
>> Any hint is welcome.
>>
>> Thanks in advance,
>> Jerome
>>
>
> It's important to realize that D does not have generics; rather, it has templates. What (alias pred, T) means is that it takes (virtually) any argument as the first template parameter (function literals included) and a type for the second parameter.
>
> You can call this function like so:
>
> auto ints = find!((x) { return x % 2 != 0; })([1, 2, 3, 4, 5]);
>
> Here, the type parameter T gets deduced from the argument, which is an array of ints.

I am certainly still very confused here, but I guess it is important I get the point before to gig further D:
In (alias pred, T), are both `pred' and `T' parameters for the function find ? or is `T' some kind of parameter for `pred' ?

Thanks in advance,
Jerome  

>