🚀 go-pugleaf

Użytkownik "A.L." <fela@2005.com> napisał:

> Bylo o tym pisane przy okazji wywiadu z jednym z C++/MS gurus albo w
> czasopismie Dr. Dobbs Journal albo Programming Languages (oba juz nie
> istnieja, niestety) bardzo dawno temu. Mam w piwnicy, ale pardon, nie
> bede szukal w ktorym numerze...

Odpryski niegdysiejszych dyskusji/sporow o NIHL

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That remark leads straight into this month's next C++ book, the long-awaited 
Data Abstraction and Object-Oriented Programming in C++ by Keith Gorlen, 
Sanford Orlow, and Perry Plexico. Gorlen et al. discuss how to stretch C++ 
as far as it will go in the direction of object-oriented languages such as 
Smalltalk, and away from the language's machine-oriented C heritage. This 
book is based on the the NIH Class Library, a Smalltalk-like class library 
for C++, which the authors developed as part of a project involving 
biomedical research on Unix-based workstations at the National Institutes of 
Health (NIH).

The NIH Class Library addresses a very real problem: C++ compilers do not 
come with extensive class libraries. If you need a LinkedList class, you 
write it (or borrow the one from Shapiro's book!). If you want the += 
operator to signify concatenation when applied to a string, then you have to 
write a String class with an operator+=( ) member function. C++ gives you 
the mechanisms, but after that you're on your own. Fundamentally, C++ is 
still C. C++ programmers can be jealous of programmers using object-oriented 
languages such as Smalltalk, which come with extensive class libraries. When 
you buy Digitalk Smalltalk/V, you get a massive class hierarchy. When you 
buy a C++ compiler, you get iostream.h. I am convinced that this Spartan 
approach, remaining true to the language's C origins, is precisely why C++ 
has succeeded. It is a compromise between C on the one hand and 
object-oriented programming on the other.

But that doesn't change the fact that you need a class library. The NIH 
Class Library brings some of the flavor of Smalltalk to C++; its class 
hierarchy has Object at the top, a Collection class underneath that, a Bag 
class underneath that, and so on. If you have Turbo C++ or the newer Borland 
C++, note that the sample CLASSLIB is a scaled-down implementation of this 
same idea.

>From the guided tour of the NIH Class Library given by Gorlen et al., I got 
the sense that C++ provides just enough object-oriented features to be 
tempting, but not enough to really work. How could it? C++ is still C. For 
example, the constructor for a BigInt class must nonintuitively take a 
string of digits because "this is the only way we can legally write very 
large integer constants in C++" (p. 34). You can't write BigInt n = 
18446744073709551615 because that number has 20 digits and is not a legal 
integer constant in C--I mean, C++. Nor can you overload operator^( ) to 
mean exponentiation and check if (n== 2^64 - 1) because in C--I mean in C++, 
the ^ operator is unary not binary.

This sort of restriction means that the promises of C++ often can't be 
fulfilled. One promise is that with operator overloading, we can give "an 
easily readable, 'mathematical' appearance" to mathematics programs (p.96). 
I believe that the NIH Class Library comes as close as possible to this 
goal, but it can't succeed, because C++ does not provide a free-form 
collection of overloadable operators.

C++ seems to hold out the promise of working at a higher level, only to pull 
you up short at the last minute with a stern reminder that this is still C. 
Restrictions of this sort are necessary if C++ is to remain a serious tool 
for developing commercial software. The authors of the NIH Class Library 
show what can be done within these restrictions. In addition to reading 
their book, you can get the NIH Class Library source code, either from the 
publisher (an additional $16.95) or by downloading it from BIX (listings 
area c.plus.plus; files nih30.zip, nih30.inf, and cppoops.zip). This is 
probably the largest collection of public C++ source code available, and is 
well worth examining.
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AK