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digitalmars.D.learn - Re: Tuple basics

reply Sam Hu <samhu.samhu gmail.com> writes:
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
Sep 12 2008
parent reply downs <default_357-line yahoo.de> writes:
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
Sep 12 2008
parent reply downs <default_357-line yahoo.de> writes:
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))
}
Sep 12 2008
parent reply downs <default_357-line yahoo.de> writes:
downs wrote:

 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




 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.



Er, the struct'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))
 }



Something else to keep in mind:

A tuple has no "binding power" of its own.

Some people get confused when they compare LISP tuples and D tuples. It is
important to keep in mind that a tuple is not a single expression.

For instance:

Tuple!(Tuple!(int, int), int)

is _EXACTLY_ the same thing as Tuple!(int, int, int)

I actually think this might be why the D specs use the term "sequence", and not
"list". A list suggests a distinct element. A sequence is just some things
following one another.
Sep 12 2008
parent Sam Hu <samhu.samhu gmail.com> writes:
Hi downs,

Thanks so much for your further explanations although I am COMPLETELY confused
at this moment,not becoz your explanation,but my stupid I think,-:)

Sam
Sep 12 2008