[Issue 4500] scoped moves class after calling the constructor

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4500


Max Samukha <samukha at voliacable.com> changed:

           What    |Removed                     |Added
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                 CC|                            |samukha at voliacable.com


--- Comment #2 from Max Samukha <samukha at voliacable.com> 2010-07-26 01:59:01 PDT ---
I didn't know D structs were allowed to be moved without calling the copy
constructor. Is it really the case?

FWIW, modern C++ implementations would optimize the copy out. For example, the
following C++ test passes with a recent GNU C++:

template <typename T>
class Scoped
{
    char data[sizeof(T)];

public:
    T* payload() { return reinterpret_cast<T*>(data); }

    Scoped(int i) { new(payload()) T(i); }

    ~Scoped() { payload()->~T(); }
};

template <typename T>
Scoped<T> scoped(int i)
{
    Scoped<T> s(i);
    return s;
}

class A {
public:
    A() { a = this; }
    A(int i) { a = this; }
    A *a;
    void check() { std::cout << (this == a ? "true" : "false") << std::endl; }
    ~A() { std::cout << "~A dtor" << std::endl; }
};

int main(int argc, char *argv[])
{
    Scoped<A> a2 = scoped<A>(1);
    a2.payload()->check(); // ok
}

Anyway, it is not reasonable to base a fundamental feature like 'scoped' on RVO
without having the latter in the language specification.

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