On 10/24/14 10:49 AM, Shriramana Sharma via Digitalmars-d-learn wrote:
Hello. I realize the wording "non-const method" is probably a C++-ism
but please see the following code. In both C++ and D, the compilers
are complaining only when I try to assign directly to the member of an
rvalue, but if I try to assign via a non-const ref returned by a
non-const method, then it's apparently fine?!! At least shouldn't D
prohibit this? [Yet another case of rvalue refs being allowed to
escape?]
nonconst.d:
--
struct Pair {
int x, y ;
ref Pair handle() { return this ; }
}
void main () {
Pair(1, 2).x = 5 ;
Pair(1, 2).handle.x = 5 ;
}
--
nonconst.cpp:
--
struct Pair {
int x, y ;
Pair(int x, int y) : x(x), y(y) {}
Pair & handle() { return *this ; }
} ;
int main () {
Pair(1, 2).x = 5 ;
Pair(1, 2).handle().x = 5 ;
}
As a matter of practicality, rvalues are allowed to bind to the 'this'
parameter of a method. I agree it's a large hole in the current
philosophy of not letting rvalues bind to references.
Most irritatingly, are things that are typically only values, and don't
have any references.
For example:
struct S
{
int v;
S opBinary(string op)(ref const(S) s2) const if(op == "+")
{
return S(v + s2.v);
}
}
void main()
{
auto s = S(2);
// auto s2 = s + S(3); // fails
auto s2 = S(3) + s; // OK
}
-Steve
