🚀 go-pugleaf

dak <pierreba@poster.cae.ca> writes:
	...
>	A a4 = new (88,91) A; // auto A object with overloaded new.
	...
>As can be seen, the syntax does not break any existing code since it is
>currently illegal to assign the result of a new operation to the declared
>variable when the pointer types are not compatible (point 1). The syntax

This is not necessarily true.  If class A has a constructor accepting
an A* argument, or some other related cases (e.g., A publically derives
from B and has a constructor accepting a B* argument), and operator new
has an overloaded version (global or class-specific) accepting two extra
int arguments, then the expression you propose is not currently illegal.
It is not immediately clear whether the resulting ambiguity can be solved
in a totally satisfactory way.

Note that an A constructor taking a B* argument, with A publically
derived from B, is quite idiomatical in envelope/letter, aka 'handle',
idioms, a la:

class Foo_abstract {
public: virtual void Bar() const = 0;
        static Foo_abstract * DefaultFooFactory();
        // etc
};

class Foo_envelope: public Foo_abstract {
    Foo_abstract *letter;
public:
    Foo_envelope(Foo_abstract *p=0): letter(p) {
       if(!letter) letter=DefaultFooFactory();
    }
    virtual void Bar() const { letter->Bar(); }
    // etc
};


Alex
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