🚀 go-pugleaf

> >For example, if you want to
> >manipulate character strings, you can use either Smalltalk strings or
> >C strings; the two kinds of strings obey different rules, and you might
> >occasionally have to worry about converting between the two string formats.
> >
> 
> This also is bogus.  I quote from the Objective-C reference manual:
> 
> 	Strings are used to hold a null-terminated array of ASCII characters
> 	(ie. by conventional C usage, " a string".
> 
> There is a structure more complex than just a "char *" that defines strings, 
> but this is true in both C++ and Objective-C.  See pages 184-185 in the
> Stroustrup C++ book for an example of this.
> 
> To create a string object initialized to "Object-Oriented Programming" in C++ 
> or Objective-C the syntax is as follows:
> 
> 	C++
> 		myString = string("Object-Oriented Programming")
> 
> 	Objective-C
> 		myString = [ String str:"Object-Oriented Programming" ];
> 
> 

In C++ you can define a class String to implement dynamic character
strings.  The data structure chosen can be much more complex than a
char*.  If properly done, you can create an initialized String as
follows:

		String myString = "Object-Oriented Programming";

But here's the part you can't do in Objective-C -- you can define implicit
type conversions for class String; in particular, you can define the
constructor:

		String::String(const char*);

Which the compiler will call automatically to convert char*s to Strings, and
you can define the member function:

		String::operator const char*();

which the compiler will call automatically to convert Strings to
char*s.  Thus, if you have a function foo(String), you can write
foo("Hello, world") -- C++ recognizes that foo() needs a String as its
argument and calls your constructor to make one from the char* "Hello,
world".  Similarly, you can use your Strings in place of char*s:

		if (strcmp(myString,"hello") == 0)

[Actually, a C++ programmer would overload ==, !=, >, and so on to do String
comparisons; e.g., you would write: if (myString == "hello")]

This feature lets a programmer blend the data structures used for his own
objects with those needed by the environment.

Another important point is what you HAVE to do in Objective-C that you
often don't in C++: free the string when your'e done with it:

Objective-C:

	foo()
	{
		id myString;
 		myString = [ String str:"Object-Oriented Programming" ];
//	code that uses myString
		[myString free];	// free the String
	} 
 
C++:
	foo()
	{
		String myString = "Object-Oriented Programming";
//	code that uses myString
	} 

C++ understands that myString is an auto, and frees it automatically
when it goes out of scope.

> In summary, both languages have what it takes to be an object-oriented 
> language.  Objective-C uses a Smalltalk-based syntax and C++ uses something
> akin to Simula syntax.  As with all programming languages, what is do-able in
> Objective-C is do-able in C++, or even C for that matter.

Talking about what is do-able is pointless -- any language with the
power of a Turing machine can do anything, theoretically.  The
question is what things does a language make it easy and pleasant to
do.  C++ features such as strong type checking and references make it
a better C for those not doing O-OP.  Features such as classes,
function and operator overloading, user-controlled implicit type
conversion, and guaranteed initialization/finalization make it far
better for programming with abstract data types than Objective-C or
Modula-2, for example.  And derived classes and virtual functions make
C++ as good or better than Objective-C for O-OP.

> I will mention though, that Objective-C has a source-level debugger 
> for it, called Vici.

What C++ currently lacks are the symbolic debugger and the extensive,
mature, supported class library that Objective-C has.  But these are
just a matter of time.



-- 
	Keith Gorlen			phone: (301) 496-5363
	Building 12A, Room 2017		uucp: uunet!mimsy!elsie!nih-csl!keith
	National Institutes of Health
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