Table of Contents Previous Section

A Note to Objective-C Developers

WebScript uses a subset of Objective-C syntax, but its role within an application is significantly different. The following table summarizes some of the differences.

Objective-C	WebScript
Supports primitive C data types	Only supports the id data type
Requires method prototyping	Doesn't require method prototyping (that is, you don't declare methods before you use them)
Usually includes a .h and a .m file	Usually has corresponding declarations and HTML template files (unless it is an application script)
Supports all C language features	Has limited support for C language features; for example, doesn't support structures, pointers, enumerators, or unions
Methods not declared to return void must include a return statement	Methods aren't required to include a return statement
Has preprocessor support	Has no preprocessor support---that is, doesn't support the #import or #include statements

Perhaps the most significant difference between Objective-C and WebScript is that in WebScript, the only valid data type is id. Some of the less obvious implications of this are:

• You can't use methods that take non-object arguments (unless those arguments are integers or floats, which WebScript converts to NSNumbers). For example, in WebScript the following statement is invalid:

  	// NO!! This won't work.  
  	string = [NSString stringWithCString:"my string"];

• You can only use the "at sign" character (@) as a conversion character with methods that take a format string as an argument:

  	// This is fine.
  	[self logWithFormat:@"The value is %@", myVar];
  	// NO!! This won't work.
  	[self logWithFormat:@"The values are %d and %s", var1, var2];

• You shouldn't supply any type information for a method's arguments and return types. These types are assumed to be id, and if you supply any type information, you will get an error.

  	// This is fine.
  	- aMethod:anArg {
  	// NO!! This won't work.
  	- (void) aMethod:(NSString *)anArg {
  	// This won't work either
  	- (id)aMethod:(id)anArg {

• You need to substitute integer values for enumerated types.
  

For example, suppose you want to compare two numeric values using the enumerated type NSComparisonResult. This is how you might do it in Objective-C:

  	result = [num1 compare:num2];  
  	if(result == NSOrderedAscending)            /* This won't work in WebScript */
      	/* num1 is less than num2 */

But this won't work in WebScript. Instead, you have to use the integer value of NSOrderedAscending, as follows:

  	result = [num1 compare:num2];  
  	if(result == -1)  
      	/* num1 is less than num2 */

For a listing of the integer values of enumerated types, see the "Types and Constants" section in the Foundation Framework Reference.

Table of Contents Next Section