Re: Compiler chooses conv ctor - why?

"Alex Blekhman" <>
Mon, 14 Apr 2008 13:54:34 +0300
"Cezary H. Noweta" wrote:

4. According to 13.3.3[1] we start at checking of parameter
conversion sequences, when selecting the best function. A
parameter of conv ctor is ,,const A&'', and implicit object
parameter of conv foo is ,,const A&'' too. Both of functions
require the same qualification conversion, thus both of them are
indistinguishable from each other.

Your analysis is correct. All I can add is that
reiterates what is said in 13.3.3/1:

Note: this argument will be compared against the first parameter
of the constructors and against the implicit object parameter of
the conversion functions.

Actually, it's a long-standing bug in VC++ that direct
initialization is not distinguished from copy initialization. The
following code demonstrates it:

struct Y {};

class X
    X() {}
    X(Y) {}
    X(const X&);

int main()
    Y y;
    X x1 = y; // ill-formed, inaccessible cctor
    X x2(y); // OK, direct initialization

    return 0;

According to the standard `x1' instance cannot be constructed due
to inaccessible copy constructor (which may be eliminated during
construction of an object by the compiler, but the copy semantics
must be preserved anyway).


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