Jonathan M Davis:
So, this really makes no sense to me at all.
I agree that foobar examples aren't so good. But it's true that
Tuple() gives some troubles regarding missed structural typing:
import std.stdio, std.typecons;
alias Tuple!(float, float) T1;
alias Tuple!(float,"x", float,"y") T2;
void foo1(T1 t) {}
void foo2(T2 t) {}
void main() {
auto p1 = T1(1, 2);
auto p2 = T2(1, 2);
p1 = p2; // no error
p2 = p1; // no error
T1[] a1;
T2[] a2;
a1 = a2; // error
a2 = a1; // error
foo1(p2); // error
foo2(p1); // error
}
Generally I think "p1 = p2;" is OK, while "p2 = p1;" is not so
good, because T2 is more specialized.
There are several other more or less similar things related to
structural typing of tuples that a well implemented built-in
tuple type will need to address. In Bugzilla there are some open
bug reports on similar matters. Fixing them with the library
defined tuples is hard. Of course a possible solution is to
improve the D language to allow the programmer to specify very
good struct-based tuples in library code, I think but doing this
is more complex than implementing good built-in tuples.
Bye,
bearophile
