cpp/types/is constant evaluated

Detects whether the function call occurs within a constant-evaluated context. Returns if the evaluation of the call occurs within the evaluation of an expression or conversion that is ; otherwise returns.

While testing whether initializers of following variables are, compilers may first perform a trial constant evaluation of the initializers:
 * variables with reference type or const-qualified integral or enumeration type
 * if the initializers are constant expressions, the variables are
 * static and thread local variables
 * if when all subexpressions of the initializers (including constructor calls and implicit conversions) are s, is performed, which can be asserted by.

It is not recommended to depend on the result in this case.

Parameters
(none)

Return value
if the evaluation of the call occurs within the evaluation of an expression or conversion that is manifestly constant-evaluated; otherwise.