[llvm-commits] CVS: llvm/include/Support/type_traits.h

[Chris Lattner]

Changes in directory llvm/include/Support:

type_traits.h added (r1.1)

---
Log message:

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!


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Diffs of the changes:  (+54 -0)

Index: llvm/include/Support/type_traits.h
diff -c /dev/null llvm/include/Support/type_traits.h:1.1
*** /dev/null	Mon Feb 23 21:50:11 2004
--- llvm/include/Support/type_traits.h	Mon Feb 23 21:49:29 2004
***************
*** 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 at 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