(WifiS3 WiFiClient) Reduce memory allocations

[ondra-novak]

Embedded devices should avoid to use memory allocation - or limit allocations to minimum. Unfortunately, the code for WiFi does not honour this rule.

• don't use std::string, use static allocated buffer
• don't use std::make_shared - we have C++17, implementing copy constructors for every class is no longer required. WiFiClient can have preallocated buffer as member variable. The programmer can possibly choose to use std::make_shared for the whole WiFIClient instance, if it needs to share it by other objects.
• typo: destroy_at_distructor
• bug: the flag destroy_at_distructor is never used, destructor is empty.

ArduinoCore-renesas/libraries/WiFiS3/src/WiFiClient.cpp

Line 6 in 03b4a91

WiFiClient::WiFiClient() : _sock(-1), destroy_at_distructor(true), rx_buffer(nullptr) {

[JAndrassy]

The programmer can possibly choose to use std::make_shared for the whole WiFIClient instance, if it needs to share it by other objects.

no. this is Arduino not C++ 17. WiFiClient must be copyable in Arduino. for example server.available and server.accept return a copy.

please add to the title that this is about the WiFiS3 library. this platform has two WiFi libraries

[ondra-novak]

Arduino is shipped with GCC-7 which defaults to C++17

for example server.available and server.accept return a copy

This is simple not true. Please learn C++
https://en.cppreference.com/w/cpp/language/copy_elision