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

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.

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

alias T = TypeTuple!(int, bool);
static assert(is(T[0] == int));

or

alias T = Tuple!(int, bool);
static assert(is(typeof(T.expand)[0] == int));

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.

On Friday, 1 August 2014 at 11:39:27 UTC, John Colvin 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
>
> alias T = TypeTuple!(int, bool);
> static assert(is(T[0] == int));
>
> or
>
> alias T = Tuple!(int, bool);
> static assert(is(typeof(T.expand)[0] == int));

Thanks.

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);

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

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.

In addition to what John Colvin posted, I'd like to add that user defined types have a 'tupleof' property. (This is yet another kind of tuple, sigh).

An example:

struct S1
{
  int i;
  string s;
}

struct S2
{
  int someInt;
  string someString;
}

void main()
{
  // A foreach loop over these kind of tuples is always expanded during
  // compilation due to their nature
  foreach(T; typeof(S1.tupleof))
  {
    // Here 'T' _is_ a type, not an instance of a type
    pragma(msg, T); // Will print 'int' and 'string' during compilation
  }

  S1 s1;
  S2 s2;

  // A way to copy one struct's values over to another of a different type,
  // but with the same layout:
  foreach(i, value; s1.tupleof)
  {
    s2.tupleof[i] = value;
  }
}