Apple WebObjects 3.5 Bedienungsanleitung PDF herunterladen (Seite 167)

WebScript Language Elements

167

In these declarations, id is a data type. The id type is a reference to any

object—in reality, a pointer to the object’s data (its instance variables). Like

a C function or an array, an object is identiﬁed by its address; thus, all

variables declared in WebScript are pointers to objects. In the examples

above,

myVar1 and myVar2 could be any object: a string, an array, or a custom

object from your application.

Note: Unlike C, no pointer manipulation is allowed in WebScript.

Instead of using

id, you can speciﬁcally refer to the class you want to

instantiate using this syntax:

className *variableName;

For example, you could specify that a variable is an NSString object using

this syntax:

NSString *myString1;

NSString *myString1, *myString2;

For more information on specifying class names in variable declarations, see

the section “Data Types” (page 174).

In WebScript, there are two basic kinds of variables: local variables and

instance variables. You declare instance variables at the top of the ﬁle, and

you declare local variables at the beginning of a method or at the beginning

of a block construct (such as a

while loop). The following shows where

variables can be declared:

id instanceVariable; // An instance variable for this class.

- aMethod {

id localVariable1; // A local variable for this method.

while (1) {

NSString *localVariable2; // A local variable for this block.

}

Variables and Scope

Each kind of variable has a different scope and a different lifetime. Local

variables are only visible inside the block of text in which they are declared.

In the example above,

localVariable1 is declared at the top of a method. It is

accessible within the entire body of that method, including the

while loop. It

is created upon entry into the method and released upon exit.

localVariable2,

on the other hand, is declared in the

while loop construct. You can only access

it within the curly braces for the

while loop, not within the rest of the method.

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