= Usage of {cpp} within RNP

This is a provisional document reflecting the recent conversion from C
to {cpp}. It should be revisited as experience with using {cpp} within RNP
codebase increases.

== Encouraged Features

These are features which seem broadly useful, their downsides are minimal
and well understood.

 - STL types std::vector, std::string, std::unique_ptr, std::map

 - RAII techniques (destructors, smart pointers) to minimize use of
   goto to handle cleanup.

 - Value types, that is to say types which simply encapsulate some
   data.

 - std::function or virtual functions to replace function pointers.

 - Prefer virtual functions only on "interface" classes (with no data),
   and derive only one level of classes from this interface class.

 - Anonymous namespaces are an alternative to `static` functions.

== Questionable Features

These are features that may be useful in certain situations, but should
be used carefully.

 - Exceptions. While convenient, they do have a non-zero cost in runtime
   and binary size.

== Forbidden Features

These are {cpp} features that simply should be avoided, at least until a
very clear use case for them has been identified and no other approach
suffices.

 - RTTI. This has a significant runtime cost and usually there are
   better alternatives.

 - Multiple inheritance. This leads to many confusing and problematic
   scenarios.

 - Template metaprogramming. If you have a problem, and you think
   template metaprogramming will solve it, now you have two problems,
   and one of them is incomprehensible.