Fast implementation of a key-value store. Environments are commonly
used as key-value stores, but every time a new key is used, it is
added to R's global symbol table, causing a small amount of memory
leakage. This can be problematic in cases where many different keys
are used. Fastmap avoids this memory leak issue by implementing the
map using data structures in C++.

WWW: https://cran.r-project.org/web/packages/fastmap/