Original idea and implementation by Benedict Cohen.

JREnum is a macro that automates creation of functions that blast enums from boring primitive compile-time-land to the fun-filled party environment of runtime.

Let's use a concrete example. Instead of writing:

typedef enum {
    Stream_Disconnected,
    Stream_Connecting,
    Stream_Connected,
    Stream_Disconnecting
}   StreamState;

write:

JREnum(StreamState,
       Stream_Disconnected,
       Stream_Connecting,
       Stream_Connected,
       Stream_Disconnecting);

This will generate the previous typedef enum and will also generate a corresponding suite of functions:

NSString* StreamStateToString(int value)

Given a value, will return the enum's string representation. For example StreamStateToString(2) would return @"Stream_Connecting".

When confronted with values not defined in the enumeration, this function will return a placeholder string explaining the situation. For example StreamStateToString(2000) would return @"<unknown StreamState: 2000>".

BOOL StreamStateFromString(NSString *enumLabel, StreamState *enumValue)

Attempts to return the enum's int value given its label. For example StreamStateFromString(@"Stream_Disconnecting", &value) would return YES and set value to 3.

This function returns NO if the label for the enum type is unknown. For example StreamStateFromString(@"lackadaisical", &value) would return NO and leave value untouched.

NSDictionary* StreamStateByValue()

Returns a dictionary whose keys are the enum's values. Used by StreamStateToString().

When enums have multiple overlapping values, the current implementation exhibits last-write-wins behavior.

NSDictionary* StreamStateByLabel()

Returns a dictionary whose keys are the enum's labels. Used by StreamStateFromString(). This is the function you want if you wish to enumerate an enum's labels and values at runtime.

JREnum() is fine for when you have an enum that lives solely in an .m file. But if you're exposing an enum in a header file, you'll have to use the alternate macros. In your .h, use JREnumDeclare():

JREnumDeclare(StreamState,
              Stream_Disconnected,
              Stream_Connecting,
              Stream_Connected,
              Stream_Disconnecting);

And then use JREnumDefine() in your .m:

JREnumDefine(StreamState);

You can also explicitly define enum integer values:

JREnum(StreamState,
       Stream_Disconnected = 42,
       Stream_Connecting,
       Stream_Connected,
       Stream_Disconnecting);

In the above scenario, Stream_Disconnected's value will be 42, Stream_Connecting's will be 43 and so on.

JREnum currently only supports integer explicit values (bit shifts and masks won't work). Patches welcome.

• Minor bug fix from 0.2.

• [NEW] Generalized to support bidirectional enum label/value lookup and full runtime access to lookup dictionary.
• [NEW] Add passing tests.
• [NEW] Write this README.

• [NEW] Devised way to allow split declaration/definition macros to allow use in header/source files.

• I publish a Ruby script to automate the generation of NSStrings from an enum declaration.
• Benedict Cohen tweets his macro idea and implementation to me.