Change _C template parameter. Cygwin ctype.h use it as macro.

include/utl/meta/if.h

@@ -31,9 +31,9 @@
 //! @{
 namespace utl {
 
-   //! select _T1 or _T2 based on _C
+   //! select _T1 or _T2 based on _Sel
    //! @{
-   template <bool _C, typename _T1, typename _T2>
+   template <bool _Sel, typename _T1, typename _T2>
    struct select_ {
       typedef _T1 type;
    };
@@ -44,9 +44,9 @@ namespace utl {
    };
    //! @}
 
-   //! select _Tp if _C is true, else SFINAE
+   //! select _Tp if _Check is true, else SFINAE
    //! @{
-   template <bool _C, typename _Tp = void>
+   template <bool _Check, typename _Tp = void>
    struct if_ {
       typedef _Tp type;
    };

include/utl/meta/sfinae.h

@@ -55,16 +55,16 @@ namespace utl {
    //! @}
 
    //! Alias template for if_
-   template<bool _C, typename _Tp = void>
-   using if_t = typename if_<_C, _Tp>::type;
+   template<bool _Check, typename _Tp = void>
+   using if_t = typename if_<_Check, _Tp>::type;
 
    //! Publicly recognized alias template for if_
-   template<bool _C, typename _Tp = void>
-   using enable_if_t = typename if_<_C, _Tp>::type;
+   template<bool _Check, typename _Tp = void>
+   using enable_if_t = typename if_<_Check, _Tp>::type;
 
    //! Uniform alias template for if_
-   template<bool _C, typename _Tp = void>
-   using use_if_t = typename if_<_C, _Tp>::type;
+   template<bool _Check, typename _Tp = void>
+   using use_if_t = typename if_<_Check, _Tp>::type;
 
    //! If same type resolves to _Ret, else SFINAE
    template <typename _T1, typename _T2, typename _Ret =_T1>