Tuple basics

[downs]

downs wrote:
> Sam Hu wrote:
>> Hi downs,
>>
>>  A Tuple [...] is a sequence of any mix of types, expressions or symbols.
>>
>> So is it a class or a type or a variable or something else?The examples in the D Spec. is used inside a template,so is it just limited to use inside  the template or can use in a common function or anywhere else?
>> Thanks,
>> Sam
> 
> It's a tuple; i.e. neither of the above.
> 
> And now you'll ask "What is a tuple?"
> 
> And the answer is still, a sequence of types, expressions or symbols.
> 
> :p

To pre-empt further questions; they appear in relation with templates because that's one of the most common ways to form type tuples:

template Tuple(T...) { alias T Tuple; }

In this case, most tuples formed this way will be type tuples, i.e. sequences of types.

For another example, the ".tupleof" expression of, say, a struct or a class evaluates to a tuple (sequence) of the values of the tuple's members.

The typeof([struct tuple]) is again a type tuple.

Look at it like this: a [X] tuple is a list, or sequence, of [X].

A type tuple is a list of types. A value tuple is a list of values.

Example (untested):

template Tuple(T...) { alias T Tuple; }

int add(int a, int b) { return a + b; }

struct Pair(T) { T a, b; }

void main() {
  Pair!(int) p; p.a = 2; p.b = 2;
  static assert(is(typeof(p.tupleof) == Tuple!(int, int)));
  // and a value tuple is a list of values
  assert(4 == add(p.tupleof)); // == assert(4 == add(/* just a list of values */ 2, 2))
}