[CLN-list] modular polynomials

[Bruno Haible]

Hello Alexei,

> > And in CLN these simple assignments are only copying a simple reference,
> > not the deep contents (see the other mail).
> 
> In C++ "deep copying" is typically called operator=.

Rather, in C++, "deep copying" is the default for operator= and copy constructor.
In those areas where this is not appropriate, people use "smart pointers".
I did not invent this idiom. It is widely used.

The reasons why CLN uses smart pointers for everything are:

1) Its main purpose is to allow the formulation of mathematical algorithms
   directly in C++. As in a scripting language. Without requiring the
   programmer to think in terms of memory allocation. The programming model
   of a scientist in this case is to manipulate opaque values that are
   elements of rings. CLN brings the philosophy of computer algebra
   languages into C++.

2) When you do computations with polynomials, you need a maximum of sharing
   of the polynomial representations. This is the basic implementation
   principle of Maple. In systems where deep copying of polynomials is the
   default, you cannot do computations as large as those possible in Maple
   - because you run out of memory earlier.

In this light, set_coeff and finalize must be implemented as copy-on-write
operations: create a deep copy implicitly when the reference count is > 1.
No explicit method for deep copying is then needed at all.

Bruno