-----Original Message----- From: edu-sig-bounces@python.org [mailto:edu-sig-bounces@python.org] On Behalf Of Jan Claeys Sent: Tuesday, September 12, 2006 2:37 PM To: edu-sig@python.org Subject: Re: [Edu-sig] Compatibility and legacy in language evolution

Op za, 09-09-2006 te 17:53 -0700, schreef Radenski, Atanas:

...

Strictly speaking this is true, but Mr. Stroustrups own papers also explain how important the full C/C++ compatibility is - and that achieving it is his ideal

Well, strictly speaking language A can only be fully compatible with language B and have more features if language B has a mechanism for extension that ignores unknown features. Considering that C has no such mechanism, C++ will never be 100% compatible with C.

Well, compatibility can be defined in *various* ways of course. If one is an extremist regarding compatibility, one can say that C++ is not compatible with itself. Indeed, the same C++ program may behave differently under different compilers - for the simple reason that some language features, particularly those related to integer types, are left implementation-dependent. The same program may run correctly under one compiler and misbehave under another. Hence - C++ is incompatible with itself. What matters in my opinion is not extremism, but a practical compatibility, as already explained by Joshua Zucker: "... a C programmer can start writing C++ programs without having to change anything -- legal C programs will still run just fine in C++. Then the C programmer can gradually learn whatever parts of the extensions of C++ at whatever rate, and slowly evolve into a C++ programmer. " Thinking of it, this kind of compatibility can provide mighty support for an evolving language.

Jan Claeys

Atanas Radenski