Key

Key Class

Objects of class Key are key-value pairs. Other classes and programs can use Key objects’ names when looking up objects. The value of a key object is a reference to the value object.

Many of the Collection subclasses are composed entirely of Key objects, which act as the “glue” that maintains references to the the actual contents of the collection. See Collection.

Programs can also manipulate Key objects independently. Most of the math operators that work with collections actually work with Key objects. So it’s important to add the attribute OBJECT_IS_MEMBER_OF_PARENT_COLLECTION to a Key object when building collections. This tells Ctalk that the Key object can be used independently, as well as part of its parent collection. See Attributes.

Here’s a program that manipulates the Key objects of a collection (here, an AssociativeArray) directly. See AssociativeArray.

int main (int argc, char **argv) {

  AssociativeArray new a;
  Key new k;

  a atPut "key1", "value1";
  a atPut "key2", "value2";
  a atPut "key3", "value3";
  a atPut "key4", "value4";

  k = *a;

  while (++k)
    printf ("%s --> %s\n", k name, *k);

}

Instance Variables

value

The value is the formatted representation of a hexadecimal pointer to a memory address.

Instance Methods

+ (Integer n)

Increments the receiver by n. For a Key object, this sets the receiver to the nth successive element in a collection. The increments are numbered with ‘1’ pointing to the first member of the collection, and so on. If there are no more elements, the receiver’s value is NULL. For an example, refer to -, below.

++

Increments the receiver to point to the next Key in a collection. If the receiver is already the last item item in the collection, the value of the receiver after it is incremented is NULL. This method works as both a prefix and postfix method, and increments the receiver either before or after it is referenced, respectively.

Here is an example of how to iterate over an AssociativeArray using ++.

  AssociativeArray new a;
  Key new k;

  a atPut "key1", "value1";
  a atPut "key2", "value2";
  a atPut "key3", "value3";
  a atPut "key4", "value4";

  k = *a;

  while (++k)
    printf ("%s --> %s\n", k name, *k);

- (Integer n)

Decrements the receiver by n. For a Key object, this sets the receiver to the nth previous element of the collection that the receiver is a member of. Here is a brief example

int main () {

  AssociativeArray new a;
  Key new k;

  a atPut "1", "value1";
  a atPut "2", "value2";
  a atPut "3", "value3";
  a atPut "4", "value4";

  k = *a;
  printf ("%s --> %s\n", k name, *k);
  k = k + 3;
  printf ("%s --> %s\n", k name, *k);
  k = k - 1;
  printf ("%s --> %s\n", k name, *k);
}

Running this program produces the following output.

1 --> value1
4 --> value4
3 --> value3

--

Decrements the receiver to point to the previous Key in a collection. If the receiver is the first item in the collection, the value of the receiver after it is decremented is NULL. Like ++, this method works as both a prefix and postfix method, and decrements the receiver either before or after it is referenced, respectively.

=

If the receiver refers to an object reference (that is, preceded by a ‘*’ operator), sets the value of the receiver to the address of the argument. Otherwise, sets the receiver to refer to the argument.

getKeyObject (void)

Return the receiver.

setName (char *key_name)

Set the receiver’s name to the argument, a String object.

Note: In some cases, the object’s name is the only way that Ctalk can refer to it. In that case, the program needs to maintain an alias to the object, like an OBJECT *, so that it can refer to the object later. In the following example, the program can refer to keyObject by using key_alias_ptr, regardless of the object’s name.

Key new keyObject;
OBJECT *key_alias_ptr;
...
key_alias_ptr = KeyObject setName keyNameString;

ulink (void)

Detach the receiver object from its parent collection. The method also removes the OBJECT_IS_MEMBER_OF_PARENT_COLLECTION attribute from the receiver.