Objective-C Mapping for Dictionaries

Here is the definition of our EmployeeMap once more:

dictionary<long, Employee> EmployeeMap;

The following code is generated for this definition:

typedef NSDictionary EXEmployeeMap;
typedef NSMutableDictionary EXMutableEmployeeMap;

Similar to sequences, Slice dictionaries map to type definitions for NSDictionary and NSMutableDictionary, with the names <module-prefix><Slice-name> and <module-prefix>Mutable<Slice-name>.

As a result, you can use the dictionary like any other NSDictionary, for example:

EXMutableEmployeeMap *em = [EXMutableEmployeeMap dictionary];
EXEmployee *e = [EXEmployee employee];
e.number = 42;
e.firstName = @"Stan";
e.lastName = @"Lippman";
[em setObject:e forKey:[NSNumber numberWithLong:e.number]];

e = [EXEmployee employee];
e.number = 77;
e.firstName = @"Herb";
e.lastName = @"Sutter";
[em setObject:e forKey:[NSNumber numberWithLong:e.number]];

To put a value type into a dictionary (either as the key or the value), you must use NSNumber as the object to hold the value. If you have a dictionary that uses a Slice enumeration as the key or the value, you must insert the enumerator as an NSNumber that holds an int.

To insert a null proxy or null class instance into a dictionary as a value, you must insert NSNull.

As a convenience feature, the Objective-C mapping also allows you to insert NSNull as the value of a dictionary if the value type of the dictionary is a string, structure, sequence, or dictionary. If you send such a dictionary to a receiver, the Ice run time marshals an empty string, default-initialized structure, empty sequence, or empty dictionary as the corresponding value to the receiver, respectively.

See Also