GSL: Guidelines support library
The GSL is a small library of facilities designed to support this set of guidelines. Without these facilities, the guidelines would have to be far more restrictive on language details.
The Core Guidelines support library is defined in namespace gsl and the names might be aliases for standard library or other well-known library names. Using the (compile-time) indirection through the gsl namespace allows for experimentation and for local variants of the support facilities.
The GSL is header only, and can be found at GSL: Guidelines support library. The support library facilities are designed to be extremely lightweight (zero-overhead) so that they impose no overhead compared to using conventional alternatives. Where desirable, they can be "instrumented" with additional functionality (e.g., checks) for tasks such as debugging.
These Guidelines use types from the standard (e.g., C++17) in addition to ones from the GSL.
For example, we assume a variant type, but this is not currently in GSL.
Eventually, use the one voted into C++17.
Some of the GSL types listed below might not be supported in the library you use due to technical reasons such as limitations in the current versions of C++. Therefore, please consult your GSL documentation to find out more.
For each GSL type below we state an invariant for that type. That invariant holds as long as user code only changes the state of a GSL object using the type's provided member/free functions (i.e., user code does not bypass the type's interface to change the object's value/bits by violating any other Guidelines rule).
Summary of GSL components:
We plan for a "ISO C++ standard style" semi-formal specification of the GSL.
We rely on the ISO C++ Standard Library and hope for parts of the GSL to be absorbed into the standard library.