Apply String move semantics to reduce memory re-allocations #2119
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mikee47
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@mikee47 Maybe you can port also this change from Arduino: esp8266/Arduino@c24109f ? |
mikee47
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Oct 20, 2020
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| // Are we're after the entire contents of this stream? | ||
| if(readPos != 0 || maxLen < size) { | ||
| // No: do a regular read | ||
| return IDataSourceStream::readString(maxLen); | ||
| } | ||
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| // Move content into the String object | ||
| ensureCapacity(size + 1); // Ensure size < capacity | ||
| String s; | ||
| if(s.setBuffer({buffer, capacity, size})) { | ||
| buffer = nullptr; | ||
| readPos = 0; | ||
| size = 0; | ||
| capacity = 0; | ||
| } | ||
| return s; |
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I'm on the fence about this behaviour. It's probably correct in 99% of situations, but the safer option might be to add an overload such as size_t readString(String& s);
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but the safer option might be to add an overload such as size_t readString(String& s);
Got for it as long as the safer option does not impact compatibility, memory usage and speed.
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@mikee47 Ping me when this PR is ready. |
Provide overrides in `FileStream` and `DataSourceStream` classes. IDataSourceStream::readBytes() calls readMemoryBlock(), then seek(), by default. Classes can override one or both of these methods for more efficient operation. Applications should use whichever is more appropriate. virtualise readString() and update stream position for consistency with `Stream` method **maxLen parameter not optional**
…ve operations Add MemoryDataStream(String&&) constructor: heap allocation required only if String is using SSO mode. Add overloads to various classes to support r-values.
…tor and setString().
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Compiler may choose copy constructors if move constructors not declared noexcept. As per esp8266/Arduino@c24109f ref. - https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-move-noexcept - https://rules.sonarsource.com/cpp/RSPEC-5018?search=noexecept - https://clang.llvm.org/extra/clang-tidy/checks/performance-noexcept-move-constructor.html
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@slaff OK, I'm done with this now! |
Merged
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String::getBufferandString::setBufferto support general move operationsreadStringmethod forMemoryDataStream