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Run-Time Type Information

For this sketch I tried to implement and apply Object Oriented Programming techniques were it made sense. I had thought I might reuse the State Machine concept, and built MachineBase and StateBase to be extendable.

The different ConfigStateMachine states like ClearState implement StateBase and its references to MachineBase, but require awareness of the ConfigStateMachine in order to write to the OLED display. To do this, ClearState requires Run-Time Type Information (RTTI) so that it can dynamic_cast<> a MachineBase to ConfigStateMachine.

Many embedded systems do not support RTTI, and for this reason the Arduino compiler disables it by default. An ESP8266 can support RTTI, but to provide Arduino support, the ESP Arduino core implementation avoids its use and implements TypeConversionFunctions combined with Enums. Applied to our case, MachineBase gets a MachineType Enum. Other objects and classes can read the Enum and determine what type the MachineBase implementation it is.

I prefer use of dynamic_cast<> because I feel it helps satisfy SOLID. TODO - finish this statement.

This sketch includes both an implementation that avoids use of RTTI and one that leverages it. TODO - get the #if directives working properly to easily switch.

A file called platform.txt contains the compiler flags for a particular board. On Windows I found mine at this path: C:\Users\USERNAME\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\3.1.2\platform.txt.

I replaced the original line:

compiler.cpp.flags=-c "{compiler.warning_flags}-cppflags" {build.stacksmash_flags} -Os -g -free -fipa-pta -Werror=return-type -mlongcalls -mtext-section-literals -fno-rtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}

With this alternative that swapps the fno-rtti flag for -frtti:

compiler.cpp.flags=-c "{compiler.warning_flags}-cppflags" {build.stacksmash_flags} -Os -g -free -fipa-pta -Werror=return-type -mlongcalls -mtext-section-literals -frtti -falign-functions=4 {build.stdcpp_level} -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags} {build.mmuflags} {build.non32xferflags}

This enables RTTI with the ESP8266 and facilitates using dynamic_cast<>.