A switch-on-string-literal construct that is a nice alternative to

cascading "ifs" of strcmps/memcmps.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85459 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/StringSwitch.h

@@ -0,0 +1,83 @@
+//===--- StringSwitch.h - Switch-on-literal-string Construct --------------===/
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//===----------------------------------------------------------------------===/
+//
+//  This file implements the StringSwitch template, which mimics a switch()
+//  statements whose cases are string literals.
+//
+//===----------------------------------------------------------------------===/
+#ifndef LLVM_ADT_STRINGSWITCH_H
+#define LLVM_ADT_STRINGSWITCH_H
+
+#include "llvm/ADT/StringRef.h"
+#include <cassert>
+#include <cstring>
+
+namespace llvm {
+  
+/// \brief A switch()-like statement whose cases are string literals.
+///
+/// The StringSwitch class is a simple form of a switch() statement that
+/// determines whether the given string matches one of the given string
+/// literals. The template type parameter \p T is the type of the value that
+/// will be returned from the string-switch expression. For example,
+/// the following code switches on the name of a color in \c argv[i]:
+///
+/// \code
+/// Color color = StringSwitch<Color>(argv[i])
+///   .Case("red", Red)
+///   .Case("orange", Orange)
+///   .Case("yellow", Yellow)
+///   .Case("green", Green)
+///   .Case("blue", Blue)
+///   .Case("indigo", Indigo)
+///   .Case("violet", Violet)
+///   .Default(UnknownColor);
+/// \endcode
+template<typename T>
+class StringSwitch {
+  /// \brief The string we are matching.
+  StringRef Str;
+  
+  /// \brief The result of this switch statement, once known.
+  T Result;
+  
+  /// \brief Set true when the result of this switch is already known; in this
+  /// case, Result is valid.
+  bool ResultKnown;
+  
+public:
+  explicit StringSwitch(StringRef Str) 
+  : Str(Str), ResultKnown(false) { }
+  
+  template<unsigned N>
+  StringSwitch& Case(const char (&S)[N], const T& Value) {
+    if (!ResultKnown && N-1 == Str.size() && 
+        (std::memcmp(S, Str.data(), N-1) == 0)) {
+      Result = Value;
+      ResultKnown = true;
+    }
+    
+    return *this;
+  }
+  
+  T Default(const T& Value) {
+    if (ResultKnown)
+      return Result;
+    
+    return Value;
+  }
+  
+  operator T() {
+    assert(ResultKnown && "Fell off the end of a string-switch");
+    return Result;
+  }
+};
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_STRINGSWITCH_H