Travis Vitek wrote:
Eric Lemings wrote:
Just a brief side note. I was just reviewing this test and
noticed that
pointers are not tested though they are valid scalar types suitable for
use as integral_constant parameters. I think references may be valid
parameters also.
I'm not sure.
The first thing that jumps to mind is that a pointer is not of
'integral' type. An enumeration isn't really an integral type either,
but they are implicitly convertible to one. Pointers aren't convertible
to integral type without a cast.
According to temp.arg.nontype, a non-type, non-template template
parameter must be one of
-- an integral constant expression
-- the name of a non-type template-parameter
-- the address of an object or function with external linkage...
-- a constant expression that evaluates to a null pointer value
-- a constant expression that evaluates to a null member pointer value
-- a pointer to member
So, yes, it is legal to use a pointer as a non-type template parameter.
The issue I have is that the integral_constant<T,V> is supposed to
define an integral constant of type T with value V. Section expr.const
says that a constant expression is an integral constant expression if it
is of integral or enumeration type. An integral constant expression can
be used as an array bound, a case expression, a bit field length,
enumeration initializer, static member initializer and as integral or
enumeration non-type template arguments.
I'm pretty sure you can't use a pointer value as an array bound, case
expression, bit field length or enumeration initializer, so they aren't
really integral constants.
So I am sure you can instantiate std::integral_constant<void
(class_t::*)(), &class::method>, but I'm not sure if it something that
should be tested.
If there's an implementation technique that would make the
instantiation ill-formed then I think it should be tested.
More important, though, the standard should specify the
requirements on the template arguments. If there are no
such requirements for something as fundamental as
integral_const, either in the latest working draft or
in one of the concepts papers (such as N2622), we should
at least bring it up on the list and/or open an issue to
have the spec clarified.
Martin
Brad.
