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    <blockquote> <p>how is it legal to return any object other than Description?</p> </blockquote> <p>You can return any type that's implicitly convertible to <code>Description</code>. In this case, any numeric type can be converted to <code>bool</code> via standard conversions, then to <code>Description</code> via the non-explicit constructor.</p> <p>You could prevent this conversion by declaring the constructor <code>explicit</code>, if you like. It's a good idea to make that a habit, to avoid unexpected conversions like this one.</p> <blockquote> <p>Does this mean a C++ compiler always calls the functions' return type constructor with the arguments of the return statement??</p> </blockquote> <p>If the types don't match, and there is a suitable non-explicit constructor to use for the conversion, yes.</p> <blockquote> <p>How did I not know that before?!</p> </blockquote> <p>C++ is a complicated language. After fifteen years, I still keep finding things I didn't know.</p>
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    1. USMike Seymour
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    1. COIt really never occurred to me that "a convertable type" could mean "a type which can be passed to a constructor to form a valid object of another type". Isn't it a bit weird to say "this object is of type bool" and then convert it by saying "an object of type bool is almost the same as a Description to which a bool is passed"?? That seems completely wrong behavior to me. I would fully expect the compiler to throw an error. I'm trying to find some C++ documentation on this, but I can't find it. Do you know where I can find it?
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    2. CO@jmbeck: The weirdness comes because you've given the type an implicit conversion constructor, which specifically says it should be convertible from `bool`. As I said, make it `explicit` if that conversion doesn't make sense; then the compiler will give the error you want. (Perhaps one could argue that that should be the default; but it isn't, so you'll just have to learn to use `explicit` when appropriate). User-defined type conversions are described in C++ 12.3 if you want the gory details; they can use a non-explicit conversion constructor or operator.
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      1. USMike Seymour
    3. COI don't think of a constructor as "is used to convert from input arguments". I think of a constructor as a function which builds a specific type _from_ the input arguments. Specifying the constructor as `explicit` prevents conversions of the input arguments, such as float to int, or int to boolean. Standard conversions make sense because they describe the types as a subset or superset of each other. I don't see that same relationship with an object's constructor and the constructors input arguments.
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