On Tuesday, 14 February 2017 at 16:25:17 UTC, Andrei Alexandrescu
wrote:
On 02/14/2017 10:49 AM, Jacob Carlborg wrote:
On 2017-02-14 15:37, Andrei Alexandrescu wrote:
How are they so,
Example [1]. That signature spans 8 lines, it took me 10
seconds to find
the actual function name.
Copying here to make things easier:
Range remove
(SwapStrategy s = SwapStrategy.stable, Range, Offset...)
(Range range, Offset offset)
if (s != SwapStrategy.stable
&& isBidirectionalRange!Range
&& hasLvalueElements!Range
&& hasLength!Range
&& Offset.length >= 1);
The function name is on the first line. I think 10 seconds
would be an exaggeration of an admittedly real issue.
Example [2], 5 lines.
Copying here as well (reflowed for email):
Tuple!(InputRange1, InputRange2)
swapRanges(InputRange1, InputRange2)(InputRange1 r1,
InputRange2 r2)
if (isInputRange!(InputRange1) && isInputRange!(InputRange2)
&& hasSwappableElements!(InputRange1)
&& hasSwappableElements!(InputRange2)
&& is(ElementType!(InputRange1) ==
ElementType!(InputRange2)));
One immediate matter here is redundant parens, of which
elimination would lead to the marginally more palatable:
Tuple!(InputRange1, InputRange2)
swapRanges(InputRange1, InputRange2)(InputRange1 r1,
InputRange2 r2)
if (isInputRange!InputRange1 && isInputRange!InputRange2
&& hasSwappableElements!InputRange1
&& hasSwappableElements!InputRange2
&& is(ElementType!InputRange1 == ElementType!InputRange2));
and what steps can we take to improve them. Could you
please give a few examples on how to do things better? Thx!
-- Andrei
Well, I would prefer to have template constraints as its own
entity in
the language not not just a bunch of boolean conditions. This
has been
talked about before several times. Something like:
constraint Foo
{
void foo();
}
void bar(T : Foo)(T t);
My recollection is past discussions got stalled because the
approach is combinatorially bankrupt. How would one express the
constraints of the functions above with simple named
constraints? (Not rhetorical; please do provide an example if
possible.) Before long there is an explosion in names
("BidirectionalWithLvalueElementsAndLength", ...).
If I had my way, like so:
Tuple!(InputRange1, InputRange2)
swapRanges
(InputRange1: (InputRange, HasSwappableElements),
InputRange2: (InputRange, HasSwappableElements))
(InputRange1 r1, InputRange2 r2)
if (is(ElementType!(InputRange1) == ElementType!(InputRange2)));
Assuming I'm still having my way, the above would result in the
compiler telling me that given:
struct Foo {
enum empty = false;
enum front = 42;
}
If I tried to instantiate swapRanges!(Foo, Foo), I'd want to get
something akin to:
error: foo.Foo does not satisfy InputRange: no function
`popFront` for `foo.Foo`
For now I'm getting quite a bit of mileage from my concepts
library.
Atila
