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A minimally interesting typo-bug

 2 years ago
source link: https://quuxplusone.github.io/blog/2022/01/29/missing-tilde/
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A minimally interesting typo-bug

I just ran into some code like this in a test suite:

struct MoveOnlyWidget {
    MoveOnlyWidget(int);
    MoveOnlyWidget(const MoveOnlyWidget&) = delete;
    MoveOnlyWidget(MoveOnlyWidget&&) = default;
    MoveOnlyWidget& operator=(const MoveOnlyWidget&) = delete;
    MoveOnlyWidget& operator=(MoveOnlyWidget&&) = default;
    MoveOnlyWidget() = default;
};

I suspect that the original author intended that last line to have a ~ in front of MoveOnlyWidget — this type ends up being default-constructible when maybe it wasn’t intended to be.

It occurs to me that it would be neat if something like PVS-Studio gave a warning for a defaulted default constructor that wasn’t at the top of the class — or maybe any constructor that wasn’t grouped with the other constructors of the class. (Maybe PVS-Studio already does! I don’t know.)

Anyway, if it really mattered that MoveOnlyWidget shouldn’t be default-constructible, the original author could have enforced that by adding any one of these lines after the class’s closing brace:

static_assert(!std::is_constructible_v<MoveOnlyWidget>);
static_assert(!std::is_default_constructible_v<MoveOnlyWidget>);
static_assert(!std::default_initializable<MoveOnlyWidget>);

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