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c++stdoptional

hold reference object inside std::optional

I am having issue when trying to pass a reference object inside std::optional as a function argument.Does it not support storing reference objects ? Example -

void fun(std::optional<ClassA& obj>)

What exatly does this error mean - static_assert failed due to requirement '!is_reference

static_assert(!is_reference_v<_Tp>)

Solution

  • The cpp reference states quite clearly:

    There are no optional references; a program is ill-formed if it instantiates an optional with a reference type. Alternatively, an optional of a std::reference_wrapper of type T may be used to hold a reference.

    So use std:reference_wrapper as suggested.

    Footnote: there are movement in the cpp commitee to enable references in std::optional. We might get them in future.