On Wednesday, 13 June 2012 at 13:34:25 UTC, Nick Treleaven wrote:
On 12/06/2012 18:56, Nathan M. Swan wrote:
When writing a generic function which takes an unknown type,
the
signature is written like so:
void fun(L)(L l) if (isList!L);
While writing a generic interface is written like so:
template isList(L) {
enum bool isList = is(typeof(
(inout int _dummy=0)
The above line seems unnecessary as we have
{no_argument_lambda;} syntax - or is there a special reason why?
I'm not sure, I just found it throughout std.range
{
L l;
if (l.nil) {}
auto e = l.car;
l = l.cdr;
));
}
BTW I think Walter said we could have enum template syntax,
which would improve the above a little:
enum bool isList(L) = is(typeof(...
This doesn't seem very intuitive to me. OOP languages handle
this with
interfaces, but in D for things like ranges we often use
structs, making
it incompatible with the current "interface."
A possible enhancement is to allow structs to implement
interfaces (but this has a runtime cost, unlike using
templates).
I'm suggesting something like a "template interface", which is
compatible with all types, and serves as a placeholder for any
type for
which the body compiles:
[snip]
void fun(List!string l);
Maybe:
void fun(L:IList)(L l);
template interface IList(E) {
template interface List(E) : List {
List!E l;
E e = l.car;
}
It makes writing generic code much cleaner.
I'm not quite sure what the ': List' part means - is it just to
declare that the List struct is used below?
That List!E "inherits" from list. I'm not sure this is necessary
or not.
Maybe it would be better for the template interface body to
contain method signatures/members rather than code?
I considered that, but somethings aren't just methods. A range's
empty could be "enum empty = false", "bool empty", or "@property
bool empty". The whole point of the range interface is syntactic
similarity, though the semantics might be different.
I think it might be an interesting idea, but it would probably
need to be significantly better than the current way with
constraints to get adopted by D.
Nick
Yea, this isn't a specific proposal, just an idea put out there.
NMS
