Upsigning or downsigning

[Damian]

Is there any way to manipulate a template parameter to change its
signedness?

For example,

template <typename T>
void foo(signed T a, unsigned T b) {

}

defines a templated function that is instantiated with a base numeric
type (e.g. int or long) but is referred by signed and unsigned
variants.

Also, how do I convert a typename to signed or unsigned? For example,
if I had some variable k I wanted to cast to the unsigned variant of
type T, I'd like to be able to do

j = (unsigned_type(T))k

but I'm not sure if it's possible to do something like that. Is there
anyway to "upsign" (i.e. convert a numeric type to signed) or
"downsign" (i.e. convert a numeric type to unsigned) similar to how
one might upcast or downcast a number?

Thanks!

Damian Eads

[tragomaskhalos]

On 7 Apr, 17:40, Damian <[e-mail]:

Also, how do I convert a typename to signed or unsigned? For example,
if I had some variable k I wanted to cast to the unsigned variant of
type T, I'd like to be able to do

* *j = (unsigned_type(T))k

but I'm not sure if it's possible to do something like that. Is there
anyway to "upsign" (i.e. convert a numeric type to signed) or
"downsign" (i.e. convert a numeric type to unsigned) similar to how
one might upcast or downcast a number?

How about this ?
<code>
template<typename Tstruct sign_variants {};
#define MAKE_SVS_FOR(T) \
template<struct sign_variants<T{\
typedef T signed_t;\
typedef unsigned T unsigned_t;\
};\
template<struct sign_variants<unsigned T{\
typedef T signed_t;\
typedef unsigned T unsigned_t;\
};
MAKE_SVS_FOR(char)
// hmmm ... glossing over char vs signed char vs unsigned char ...
MAKE_SVS_FOR(int)
MAKE_SVS_FOR(long)
MAKE_SVS_FOR(short)
// add any other flavours your compiler supports

#undef MAKE_SVS_FOR

// then e.g.
#include <iostream>

const char* foo(long x)
{ return "slong"; }
const char* foo(unsigned long x)
{ return "ulong"; }

void signedness()
{
std::cout << foo(sign_variants<long>::signed_t()) << '\n';
std::cout << foo(sign_variants<long>::unsigned_t()) << '\n';
std::cout << foo(sign_variants<unsigned long>::signed_t()) << '\n';
std::cout << foo(sign_variants<unsigned long>::unsigned_t()) <<
'\n';
}
/*
output
slong
ulong
slong
ulong
*/
</code>

Obviously you'd use sign_variants inside a template.