Add macro to cast away const without allowing changes to underlying type

Enterprise / PostgreSQL - Andres Freund [anarazel.de] - 16 October 2018 19:05 EDT

The new unconsitify(underlying_type, var) macro allows to cast constness away from a variable, but doesn't allow changing the underlying type. Enforcement of the latter currently only works for gcc like compilers.

Please note IT IS NOT SAFE to cast constness away if the variable will ever be modified (it would be undefined behaviour). Doing so anyway can cause compiler misoptimizations or runtime crashes (modifying readonly memory). It is only safe to use when the the variable will not be modified, but API design or language restrictions prevent you from declaring that (e.g. because a function returns both const and non-const variables).

This'll be used in an upcoming change, but seems like it's independent infrastructure.

Author: Andres Freund Discussion: https://postgr.es/m/20181015200754.7y7zfuzsoux2c4ya@alap3.anarazel.de

d1211c63f0 Add macro to cast away const without allowing changes to underlying type.
src/include/c.h | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)

Upstream: git.postgresql.org


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