Re: Compare TypeTuple element with another type

[John Colvin via Digitalmars-d]

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);