Check in a new type_traits header which provides the mysterious is_class

template.  Thanks go out to Reid Spencer for skillfully extracting this
from boost!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11784 91177308-0d34-0410-b5e6-96231b3b80d8

include/Support/type_traits.h

@@ -0,0 +1,54 @@
+//===- Support/type_traits.h - Simplfied type traits ------------*- C++ -*-===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file provides a template class that determines if a type is a class or
+// not. The basic mechanism, based on using the pointer to member function of
+// a zero argument to a function was "boosted" from the boost type_traits 
+// library. See http://www.boost.org/ for all the gory details. 
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_TYPE_TRAITS_H
+#define LLVM_SUPPORT_TYPE_TRAITS_H
+
+// This is actually the conforming implementation which works with abstract
+// classes.  However, enough compilers have trouble with it that most will use
+// the one in boost/type_traits/object_traits.hpp. This implementation actually
+// works with VC7.0, but other interactions seem to fail when we use it.
+
+namespace llvm {
+
+namespace dont_use
+{
+    // These two functions should never be used. They are helpers to
+    // the is_class template below. They cannot be located inside 
+    // is_class because doing so causes at least GCC to think that
+    // the value of the "value" enumerator is not constant. Placing
+    // them out here (for some strange reason) allows the sizeof 
+    // operator against them to magically be constant. This is
+    // important to make the is_class<T>::value idiom zero cost. it
+    // evaluates to a constant 1 or 0 depending on whether the 
+    // parameter T is a class or not (respectively).
+    template<typename T> char is_class_helper(void(T::*)(void));
+    template<typename T> double is_class_helper(...);
+}
+
+template <typename T>
+struct is_class
+{
+  // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For
+  // more details:
+  // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1
+ public:
+    enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) };
+};
+
+}
+
+#endif

include/llvm/Support/type_traits.h

@@ -0,0 +1,54 @@
+//===- Support/type_traits.h - Simplfied type traits ------------*- C++ -*-===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file provides a template class that determines if a type is a class or
+// not. The basic mechanism, based on using the pointer to member function of
+// a zero argument to a function was "boosted" from the boost type_traits 
+// library. See http://www.boost.org/ for all the gory details. 
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_TYPE_TRAITS_H
+#define LLVM_SUPPORT_TYPE_TRAITS_H
+
+// This is actually the conforming implementation which works with abstract
+// classes.  However, enough compilers have trouble with it that most will use
+// the one in boost/type_traits/object_traits.hpp. This implementation actually
+// works with VC7.0, but other interactions seem to fail when we use it.
+
+namespace llvm {
+
+namespace dont_use
+{
+    // These two functions should never be used. They are helpers to
+    // the is_class template below. They cannot be located inside 
+    // is_class because doing so causes at least GCC to think that
+    // the value of the "value" enumerator is not constant. Placing
+    // them out here (for some strange reason) allows the sizeof 
+    // operator against them to magically be constant. This is
+    // important to make the is_class<T>::value idiom zero cost. it
+    // evaluates to a constant 1 or 0 depending on whether the 
+    // parameter T is a class or not (respectively).
+    template<typename T> char is_class_helper(void(T::*)(void));
+    template<typename T> double is_class_helper(...);
+}
+
+template <typename T>
+struct is_class
+{
+  // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For
+  // more details:
+  // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1
+ public:
+    enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) };
+};
+
+}
+
+#endif