Compare TypeTuple element with another type

[John Colvin via Digitalmars-d]

On Friday, 1 August 2014 at 12:08:23 UTC, John Colvin wrote:
> On Friday, 1 August 2014 at 11:55:02 UTC, Tudor Berariu wrote:
>> On Friday, 1 August 2014 at 10:34:02 UTC, Rene Zwanenburg 
>> wrote:
>>> On Friday, 1 August 2014 at 10:25:39 UTC, Tudor Berariu wrote:
>>>> Is it possible to compare at compile time an element from a 
>>>> TypeTuple with another type?
>>>>
>>>> This code fails:
>>>>
>>>>  alias T = Tuple!(int, bool);
>>>>  static assert(is(T[0] == int));
>>>>
>>>>
>>>>  Error: static assert  (is(Tuple!(int, bool)[0] == int)) is 
>>>> false
>>>>
>>>>
>>>> Tudor
>>>
>>> Tuple is not a type tuple, it's a runtime tuple. TypeTuple is 
>>> located in std.typetuple. Use that and your code will work.
>>
>> Thank you! That works indeed, but my problem is actually a bit 
>> different.
>> I called that a "TypeTuple" because I read this line in the 
>> documentation "If a tuple's elements are solely types, it is 
>> called a TypeTuple" (http://dlang.org/tuple.html).
>>
>> What I want to achieve is something like this:
>>
>>    template isNeededType(T) {
>>      enum bool isNeededType = is(T[0] == int);
>>    }
>>
>>    ...
>>
>>    enum auto t = Tuple!(int, bool)(3, false);
>>    alias T = typeof(t);
>>    static assert(isNeededType!T);
>>
>> I know that "is(typeof(t[0]) == int)" works for the above 
>> example, but I need to get, if possible, the types of the 
>> elements from the type of that tuple only.
>
> template isNeededType(T)
> {
>     enum isNeededType = is(T[0] == int);
> }
>
> enum t = tuple(3, false);
> alias T = typeof(t.expand);
> static assert(isNeededType!T);

sorry, that should be

template isNeededType(T ...)

also, please use http://forum.dlang.org/group/digitalmars.D.learn 
for these sort of questions