Re: Call by reference vs. call by value

[dewar@cs.nyu.edu (Robert Dewar)]

Karl asks

"This is really a C or C++ issue, but I still am not sure I understand.  I seem
to remember passing arrays as function parameters in both C and C++.  Since an
array reference is always implemented with a pointer in C and C++, all such
passing is pass by reference.  Why then do you say you can't pass arrays anyway?"


You can pass a pointer *by value* in either C or Ada or C++, but this is
NOT a call by reference. You can pass a *pointer* to an array, but not
an array itself in C, but in Ada you can pass either a pointer to an 
array (which obviously has reference semantics at the array abstraction
level, even though it is a call by value), OR you can pass an array.
It is when an array is passed, something you cannot do in C, that the
problem arises.

Why not just go to the C model of passing pointers around? you might ask!
The trouble with this approach is it requires far more aliasing than is
comfortable in a language of this class. 
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