[Octave-bug-tracker] [bug #56752] Performance slowdown from version 3.2.4 through to current dev branch

[John W. Eaton]

Follow-up Comment #47, bug #56752 (project octave):

Rik: when you write


const Array<int> new_ra (old_ra);
int elt = new_ra(1);


then you call the const elem method which doesn't need to check the reference
count because it can't modify the array.

But if you write


Array<int> new_ra (old_ra);
int elt = new_ra(1);


then the non-const elem method is called.  It returns a reference and is not
(and could not, at the time these classes were first written) be overloaded
based on whether it it is used in an rvalue or lvalue context, so it has to
check the reference count and maybe force a copy to provide COW semantics.

Now, with modern C++, is it possible to determine whether the operator is
invoked in an lvalue or rvalue context?  If so, then we could just fix this
with some changes to the Array class.  But even after reading about
ref-qualifiers and looking at some examples, I don't see how to do it.

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