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| 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 "tools/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 |
| 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_ |
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