A generic symbol table implementation supporting
pop operations which cannot be shared between threads.
For an implementation which implements
Sync at the cost of a performance penalty, see
A symbol table implementation supporting snapshots, i.e. an
A trait for a symbol table which in which entries may be infallibly mutated.
A trait for a symbol table which can be indexed by a given key.
A trait for a stack-like symbol table in which a reference to the previous layer may be obtained