Prevent optimizing out a map

[bradunov]

Is your feature request related to a problem? Please describe.

If a map is not being used, it is optimized out by the compiler. This creates problems elsewhere in the development chain, for example when linking maps (see issue #83 ).

Describe the solution you'd like

The preferred solution would be to raise an error if a map is declared but not used.
Another acceptable solution would be to allocate a map and silently ignore that it is not being used.