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gpderetta • last Tuesday at 11:07 AM • 1 reply • view on HN

First of all mem::transmute is like bit_cast (which works perfectly fine in constexpr context), not reinterpret cast.

Second, this compiles just fine:

   constexpr int ivalue = 1;
   constexpr bool bvalue {ivalue};
This fails at compile time (invalid narrowing):

    constexpr int ivalue = 2;
    constexpr bool bvalue {ivalue};
Note we don't need bit_cast for this example as int to bool conversions are allowed in C++.

Replies

tialaramex • last Tuesday at 12:54 PM

Surely "We have many different ways to do this, each with different rules" is exactly the point? C++ 20's std::bit_cast isn't necessarily constexpr by the way although it is for the trivial byte <-> boolean transmutation I mentioned here.

I see that C++ people were more comfortable with the "We have far too many ways to initialize things" examples of this problem but I think transmutation hits harder precisely because it sneaks up on you.

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