1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef TOOLS_GN_PARSE_NODE_VALUE_ADAPTER_H_ 6 #define TOOLS_GN_PARSE_NODE_VALUE_ADAPTER_H_ 7 8 #include "base/macros.h" 9 #include "gn/value.h" 10 11 class ParseNode; 12 13 // Provides a means to convert a parse node to a value without causing a copy 14 // in the common case of an "Identifier" node. Normally to get a value from a 15 // parse node you have to call Execute(), and when an identifier is executed 16 // it just returns the current value of itself as a copy. But some variables 17 // are very large (lists of many strings for example). 18 // 19 // The reason you might not want to do this is that in the case of an 20 // identifier where the copy is optimized away, the origin will still be the 21 // original value. The result can be confusing because it will reference the 22 // original value rather than the place where the value was dereferenced, e.g. 23 // for a function call. The InitForType() function will verify type information 24 // and will fix up the origin so it's not confusing. 25 class ParseNodeValueAdapter { 26 public: 27 ParseNodeValueAdapter(); 28 ~ParseNodeValueAdapter(); 29 get()30 const Value& get() { 31 if (ref_) 32 return *ref_; 33 return temporary_; 34 } 35 36 // Initializes the adapter for the result of the given expression. Returns 37 // truen on success. 38 bool Init(Scope* scope, const ParseNode* node, Err* err); 39 40 // Like Init() but additionally verifies that the type of the result matches. 41 bool InitForType(Scope* scope, 42 const ParseNode* node, 43 Value::Type type, 44 Err* err); 45 46 private: 47 // Holds either a reference to an existing item, or a temporary as a copy. 48 // If ref is non-null, it's valid, otherwise the temporary is used. 49 const Value* ref_; 50 Value temporary_; 51 52 DISALLOW_COPY_AND_ASSIGN(ParseNodeValueAdapter); 53 }; 54 55 #endif // TOOLS_GN_PARSE_NODE_VALUE_ADAPTER_H_ 56