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Halturin Evgeniy
Asked:2024-04-23 19:53:09 +0000 UTC2024-04-23 19:53:09 +0000 UTC

运行时类型选择的统一

  • 772

我需要在运行时确定具体类型。种类有固定数量，但也有很多。准确的说是256。我做了一个创客。但看起来令人毛骨悚然。

static TBase* NewObj(unsigned char num)
{
    switch (num)
    {
    case 0: return new TDerived<0>;
    case 1: return new TDerived<1>;
    case 2: return new TDerived<2>;
    case 3: return new TDerived<3>;
    case 4: return new TDerived<4>;
    case 5: return new TDerived<5>;
    case 6: return new TDerived<6>;
    case 7: return new TDerived<7>;
    case 8: return new TDerived<8>;
    case 9: return new TDerived<9>;
    case 10: return new TDerived<10>;
    case 11: return new TDerived<11>;
    case 12: return new TDerived<12>;
    case 13: return new TDerived<13>;
    case 14: return new TDerived<14>;
    case 15: return new TDerived<15>;
    // ...
    // ...
    default: return nullptr;
    }
}

没有256个案例能做到这一点吗？或者这是正常的？还是我又犯傻了？

c++

1 个回答

  1. Best Answer

    您可以将函数指针推入表中，而不是使用大小写：

    template<unsigned char num>
auto
MakeObj()
{ 
    return ::std::unique_ptr<TBase>{new TDerived<num>{}};
}

template<unsigned char... num_pack>
constexpr auto
MakeLut(::std::integer_sequence<unsigned char, num_pack...>)
{
    return ::std::array{&MakeObj<num_pack>...};
}

constexpr auto lut{MakeLut(::std::make_integer_sequence<unsigned char, 255>())};

auto NewObj(unsigned char num)
{
    return (*lut[num])();
}
    • 2

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