Add initial prototype for the GN meta-buildsystem.

tools/gn/value.h

Index: tools/gn/value.h
diff --git a/tools/gn/value.h b/tools/gn/value.h
new file mode 100644
index 0000000000000000000000000000000000000000..8802bffb157b29f9b4eaef5b3e6faf15c1af6102
--- /dev/null
+++ b/tools/gn/value.h
@@ -0,0 +1,91 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TOOLS_GN_VALUE_H_
+#define TOOLS_GN_VALUE_H_
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/strings/string_piece.h"
+#include "tools/gn/err.h"
+
+class ParseNode;
+
+// Represents a variable value in the interpreter.
+class Value {
+ public:
+  enum Type {
+    NONE = 0,
+    INTEGER,
+    STRING,
+    LIST
+  };
+
+  Value();
+  Value(const ParseNode* origin, Type t);
+  Value(const ParseNode* origin, int64 int_val);
+  Value(const ParseNode* origin, const base::StringPiece& str_val);
+  ~Value();
+
+  Type type() const { return type_; }
+
+  // Returns a string describing the given type.
+  static const char* DescribeType(Type t);
+
+  // Returns the node that made this. May be NULL.
+  const ParseNode* origin() const { return origin_; }
+  void set_origin(const ParseNode* o) { origin_ = o; }
+
+  int64& int_value() {
+    DCHECK(type_ == INTEGER);
+    return int_value_;
+  }
+  const int64& int_value() const {
+    DCHECK(type_ == INTEGER);
+    return int_value_;
+  }
+
+  std::string& string_value() {
+    DCHECK(type_ == STRING);
+    return string_value_;
+  }
+  const std::string& string_value() const {
+    DCHECK(type_ == STRING);
+    return string_value_;
+  }
+
+  std::vector<Value>& list_value() {
+    DCHECK(type_ == LIST);
+    return list_value_;
+  }
+  const std::vector<Value>& list_value() const {
+    DCHECK(type_ == LIST);
+    return list_value_;
+  }
+
+  // Returns the current value converted to an int, normally used for
+  // boolean operations. Undefined variables, empty lists, and empty strings
+  // are all interpreted as 0, otherwise 1.
+  int64 InterpretAsInt() const;
+
+  // Converts the given value to a string.
+  std::string ToString() const;
+
+  // Verifies that the value is of the given type. If it isn't, returns
+  // false and sets the error.
+  bool VerifyTypeIs(Type t, Err* err) const;
+
+  // Compares values. Only the "value" is compared, not the origin.
+  bool operator==(const Value& other) const;
+  bool operator!=(const Value& other) const;
+
+ private:
+  Type type_;
+  std::string string_value_;
+  int64 int_value_;
+  std::vector<Value> list_value_;
+  const ParseNode* origin_;
+};
+
+#endif  // TOOLS_GN_VALUE_H_