Move 'Optional' class from Clang to LLVM/ADT.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100889 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/Optional.h

@@ -0,0 +1,66 @@
+//===-- Optional.h - Simple variant for passing optional values ---*- C++ -*-=//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file provides Optional, a template class modeled in the spirit of
+//  OCaml's 'opt' variant.  The idea is to strongly type whether or not
+//  a value can be optional.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_OPTIONAL
+#define LLVM_ADT_OPTIONAL
+
+#include <cassert>
+
+namespace llvm {
+
+template<typename T>
+class Optional {
+  T x;
+  unsigned hasVal : 1;
+public:
+  explicit Optional() : x(), hasVal(false) {}
+  Optional(const T &y) : x(y), hasVal(true) {}
+
+  static inline Optional create(const T* y) {
+    return y ? Optional(*y) : Optional();
+  }
+
+  Optional &operator=(const T &y) {
+    x = y;
+    hasVal = true;
+    return *this;
+  }
+  
+  const T* getPointer() const { assert(hasVal); return &x; }
+  const T& getValue() const { assert(hasVal); return x; }
+
+  operator bool() const { return hasVal; }
+  bool hasValue() const { return hasVal; }
+  const T* operator->() const { return getPointer(); }
+  const T& operator*() const { assert(hasVal); return x; }
+};
+
+template<typename T> struct simplify_type;
+
+template <typename T>
+struct simplify_type<const Optional<T> > {
+  typedef const T* SimpleType;
+  static SimpleType getSimplifiedValue(const Optional<T> &Val) {
+    return Val.getPointer();
+  }
+};
+
+template <typename T>
+struct simplify_type<Optional<T> >
+  : public simplify_type<const Optional<T> > {};
+
+} // end llvm namespace
+
+#endif