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int i = 1; int j = 2; optional<int&> oi = i; optional<int&> oj = j; i = j;

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The effect here is that i remains 1, j remains 2 and oi and oj both hold a reference to j. You may find it less surprising but if you think of optional reference as a regular reference that is initialized a bit later, the behavior is not what you would expect.

Huh? How does oi come to hold a reference to j?

Apologies, I meant to say int i = 1; int j = 2; optional<int&> oi = i; optional<int&> oj = j; oi = oj; Boost.Optional documentation explains it better: http://www.boost.org/doc/libs/1_48_0/libs/optional/doc/html/boost_optional/r... Regards, &rzej