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(a) Doing nothing. (b) Complaining if the variable does not have that type.(c) Assuming that the variable has that type and and acting in a way that will be dangerous if it does not.
These are often offered as compilation options. They seem to offer a wider range of useful behaviour and a wider range of trade-offs between safety and optimization.
The "assertion" semantics also more naturally extend to limited ranges (e.g., asserting that an integer is non-zero) or using unions of types.
Regards, Alan -- Dr Alan Watson Centro de Radioastronomía y Astrofísica Universidad Astronómico Nacional de México