Bill Baxter wrote:
On Tue, Nov 17, 2009 at 3:57 PM, retard <[email protected]> wrote:
Tue, 17 Nov 2009 14:38:57 -0800, Bill Baxter wrote:
I agree, a tuple of one element (doesn't matter what type, array in
this case) should be semantically identical to that single element.
proper semantics for language supported tuples should IMO include: 1)
syntax to explicitly [de]construct tuples and no auto-flattening 2) a
tuple of one element is identical to a scalar:
int a = 5; // scalar integer
auto b = (5); // tuple of one integer a == b // is true
Interesting. It does kinda make sense. So should indexing work too?
And properties? 5[0] == 5? 5.length == 1? If not that could be painful
for functions that process generic N-tuples. If so then what does that
do if the "scalar" type happens to be float*?
In some languages () is a distinct Unit type. Tuples are defined
recursively from the Pair type, e.g. Pair[int,int], Pair[int, Pair
[int,int]] === (int,int,int). And have a special indexing syntax with 1-
based indexing.
That wasn't really the question. It was what should 5[0] do in D, if
scalars are considered to be 1-tuples?
I think that's a killer for 1-tuple / scalar equivalence in D.
Neither behavior is acceptable in my opinion.
So it seems you can't have 1-tuple/scalar equivalence unless you have
a distinct tuple-indexing syntax.
Right now std.typecons.tuple uses x.at!(0) because you can't have a
x[i] return different types, but the built-in "A..." template tuples
do it.
So that's something that needs to be fixed anyway, because "good for
me but not for thee" is lame. (Took that phrase from a review of
Go...)
I think probably D should allow a templated opIndex!(int) so that user
types can implement tuple-like indexing where each index could be a
different type.
Or we should try to come up with another syntax for indexing tuples.
3) function's argument list is a tuple like in ML:
void foo(int a, char b);
int a = 5; char b ='a';
auto tup = (5, 'a');
foo(a, b) is identical to foo(t);
Tuples can't encode things like by-ref, by-val, lazy etc.
That does seem to kill that idea.
That seems like a kind of auto-flattening. Shouldn't (t) be a tuple of
a tuple?
What if you have an actual tuple in the signature, like void foo((int
a,char b))?
Or you have both overloads -- foo(int,char) and foo((int,char)) I think
I like Python's explicit "explode tuple" syntax better.
foo(*t)
Probably that syntax won't work for D, but I'd prefer explicit
flattening over implicit.
Good boy.
4) unit type defined by the empty tuple instead of c-like void
This is kind of neat, but does it actually change anything? Or just
give an aesthetically pleasing meaning to void/unit?
The empty tuple can be considered to be the unit type.
Yes, Yigal said basically that. The question I have is what practical
difference does that make to the language?
Seems no different from defining the empty tuple to be void, then
renaming void to unit.
--bb
to clarify what I meant regarding function args list lets look at a few
ML examples:
fun f1() = ()
f1 is unit -> unit
fun f2 (a) = a
f2 `a -> `a
fun f3 (a, b, (c, d)) = a + b + c + d
f3 is (`a, `a, (`a, `a)) -> `a
it doesn't auto flatten the tuples but the list of parameters is
equivalent to a tuple.
regarding unit type, it has by definition exactly one value, so a
function that is defined now in D to return "void" would return that
value and than it's perfectly legal to have foo(bar()) when bar returns
a unit type.
