On Sunday, 20 July 2014 at 15:45:37 UTC, Atila Neves wrote:
On Thursday, 17 July 2014 at 22:52:37 UTC, Justin Whear wrote:
On Thu, 17 Jul 2014 22:49:30 +0000, Nordlöw wrote:
AFAIK there is no compile-time variant of interfaces right?
Why is that?
Wouldn't it be nice to say something like
struct SomeRange realize InputRange {
/* implement members of InputRange */
}
and then the compiler will statically check that that all
members are
implemented correctly.
I guess this requires some new syntax to describe what an
InputRange is.
Kind of like C++ Concepts.
What benefits would accrue from adding this? Static
verification that a
structure implements the specified concepts? If so, you can
simply do
this instead:
static assert(isInputRange!SomeRange);
This is sufficient, but not adequate. Just as the built-in
unittest blocks with assertions, it's great when the assertion
is
true but good luck finding out where the bug is when it's not.
The D Cookbook has an idiom to handle this by checking for
__ctfe
but it's super hacky and there should be a better way.
I have lost count of how many times I wish the compiler would
help me with compile time interfaces as it does with runtime
code. static override and static interface? Yes please.
Atila
+1, failing template constraints just gives a vague "couldn't
match overload" type of error, and sometimes static assertions
get suppressed. I've noticed that opDispatch is particularly bad
about this. Even syntactic errors won't trigger compiler
messages, and instead seems to behave like SFINAE which I was
assured doesn't exist in D.
I have to use pragma (msg, ...) to get meaningful errors. Its so
bad I generally avoid opDispatch despite its awesome potential
and just generate template functions with mixins instead, because
they are marginally easier to debug.
I wind up doing things like this to get the functionality I want:
static string assert_processing_stage_defined (string stage)()
{
static immutable error_msg = `"Model must define processing
stage: ` ~stage~ ` ()"`;
return q{
static assert (hasMember!(This, } `"`~stage~`"` q{), }
~error_msg~ q{);
static assert (isSomeFunction!(__traits(getMember, This, }
`"`~stage~`"` q{)), } ~error_msg~ q{);
static assert (ParameterTypeTuple!(__traits(getMember, This, }
`"`~stage~`"` q{)).length == 0, } ~error_msg~ q{);
static assert (is (ReturnType!(__traits(getMember, This, }
`"`~stage~`"` q{)) == void), } ~error_msg~ q{);
};
}
mixin(``
~assert_processing_stage_defined!`initialize`
~assert_processing_stage_defined!`update`
);
I'm sure theres worse ways to do it but I still find this ugly
and overly specific. I would much rather use something like what
Nordlöw suggested. Something that is standardized across the
language and generates meaningful error messages.
