WString: mark move ctor as noexcept by mcspr · Pull Request #7610 · esp8266/Arduino (original) (raw)

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

Move constructors of all the types used with STL containers, for
example, need to be declared noexcept. Otherwise STL will choose copy
constructors instead. The same is valid for move assignment operations.

With a basic example based on the master

diff --git a/cores/esp8266/WString.cpp b/cores/esp8266/WString.cpp index 46aad5d5..1c93d8f2 100644 --- a/cores/esp8266/WString.cpp +++ b/cores/esp8266/WString.cpp @@ -225,6 +225,7 @@ String & String::copy(const __FlashStringHelper *pstr, unsigned int length) {

#ifdef GXX_EXPERIMENTAL_CXX0X void String::move(String &rhs) {

• Serial.printf("moved! %p -> %p\n", &rhs, this); if (buffer()) { if (capacity() >= rhs.len()) { memmove_P(wbuffer(), rhs.buffer(), rhs.length() + 1);

#include <Arduino.h>

#include

void setup() { Serial.begin(115200);

std::vector<String> objects;
for (int num = 0; num < 10; ++num) {
    objects.emplace_back(num); 
}

}

void loop() { delay(1000); ESP.restart(); }

Since the vector is not using .reserve(...), we need to realloc + move existing vector contents every push when vector needs more capacity. Without the patch, we will never see the moved! string from the above.

Core does use std::vector<String> in a couple of places as well, it is not just possible user code:

git grep 'std::vector<Str'
libraries/ESP8266WebServer/src/Uri.h:        virtual bool canHandle(const String &requestUri, __attribute__((unused)) std::vector<String> &pathArgs) {
libraries/ESP8266WebServer/src/detail/RequestHandler.h:    std::vector<String> pathArgs;
libraries/ESP8266WebServer/src/uri/UriBraces.h:        bool canHandle(const String &requestUri, std::vector<String> &pathArgs) override final {
libraries/ESP8266WebServer/src/uri/UriGlob.h:        bool canHandle(const String &requestUri, __attribute__((unused)) std::vector<String> &pathArgs) override final {
libraries/ESP8266WebServer/src/uri/UriRegex.h:        bool canHandle(const String &requestUri, std::vector<String> &pathArgs) override final {

(But, I am not sure what is the implication for the overall Arduino API stuff. Does it need the patch, too, if this is valid?)