std.algorithm.find and array of needles?

[captaindet]

On 2014-03-03 16:19, John Colvin wrote:
> On Monday, 3 March 2014 at 22:03:24 UTC, captaindet wrote:
>> On 2014-03-03 14:58, John Colvin wrote:
>>> On Monday, 3 March 2014 at 19:35:53 UTC, captaindet wrote:
>>>> std.algorithm.find has an overload that works with several needles:
>>>>
>>>> // phobos doc example:
>>>> int[] a = [ 1, 4, 2, 3 ];
>>>> assert(find(a, [ 1, 3 ], 4) == tuple([ 4, 2, 3 ], 2));
>>>>
>>>> the function i want to write has to deal with variadic arguments serving as needles. unfortunately, i failed trying to make find work with the needles provided in an array:
>>>>
>>>> int[] a = [ 9, 8, 7, 6, 5, 4, 3, 2, 1 ];
>>>> int[][] ns = [ [ 7, 6 ], [ 4, 3 ] ];
>>>> auto res = find( a, ns );
>>>> //Error: template std.algorithm.find does not match any function template declaration. Candidates are:
>>>>
>>>> any ideas how this can be achieved?
>>>>
>>>> thanks
>>>> /det
>>>
>>> You can use a variadic template function instead of variadic slice construction:
>>>
>>> void foo(A, T ...)(A[] a, T ns)
>>> {
>>> //use find as follows. For example:
>>> return a.find(ns);
>>> }
>>>
>>> assert(foo([1,2,3,4], 3, 6, 2) == Tuple!([2,3,4], 2));
>>
>> thanks, john.
>>
>> i was afraid that this is the hoop i might have to jump through ;)
>>
>> which is fine for the simple case i asked for. in another case, i would need to construct a needle proper from each pre-needle that is one the variadic arguments. this seems impossible now.
>>
>> so i probably have to make the pre-needles template parameters and enter the dreadful realm of std.typetuple... guess staticMap is my friend here.
>>
>>
>> cheers
>> /det
>
> Luckily, you don't have to. foreach over tuples is awesome:
>
> import std.typecons;
> import std.algorithm;
>
> auto makeProperNeedle(T)(T needle)
> {
> //do something to needle
> return needle;
> }
>
> auto foo(A, T ...)(A[] a, T preNeedles)
> {
> Tuple!T needles;
> foreach(i, preNeedle; preNeedles)
> {
> needles[i] = makeProperNeedle(preNeedle);
> }
> //use find as follows. For example:
> return a.find(needles.expand);
> }
>
> unittest
> {
> assert(foo([1,2,3,4], 3, 6, 2) == tuple([2,3,4], 3));
> }

awesome indeed - works like a charm!

many thanks
/det