A variable with MT-access pattern "very often reads, seldom writes". It is specially optimized for reads. On read, one obtains a ReaderPtr<T> from it and uses the obtained value as long as it wants to. On write, one obtains a WritablePtr<T> with a copy of the last version of the value, makes some changes to it, and commits the result to update current variable value (does Read-Copy-Update). Old version of the value is not freed on update, it will be eventually freed when a subsequent writer identifies that nobody works with this version.
Obtain a smart pointer that will copy the current value. The pointer can be used to make changes to the value and to set the Variable to the changed value.
