[C++-sig] Non-const reference arguments and from_python conversions

[Ralf W. Grosse-Kunstleve]

> Does this mean the argument MUST be passed by const-reference or by
> value (i.e. it can't be a non-const reference or a pointer)?

Yes. -- A few years ago we had a contract with David to implement
support for "converters with write-back", but it turned out to be
too difficult.

In theory you can use indirection of some sort to get around the problem
(e.g. make a proxy object holding a reference to the object you actually want
to pass, pass the proxy by value). However, in most cases this will
probably impose unacceptable restrictions on the interface.

Ralf