JREnum
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_Connected".
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.
Split Header / Source Files
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);
Explicit Values
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.
You can also use hex values:
JREnum(StreamState,
Stream_Disconnected = 0x2A,
Stream_Connecting,
Stream_Connected,
Stream_Disconnecting);
That's semantically identical to the above.
New in v1.1 you can use very simple bit-shift masks:
JREnum(Align,
AlignLeft = 1 << 0,
AlignRight = 1 << 1,
AlignTop = 1 << 2,
AlignBottom = 1 << 3,
AlignTopLeft = 0x05,
AlignBottomLeft = 0x09,
AlignTopRight = 0x06,
AlignBottomRight = 0x0A,
);
This helps where you want one variable to house a combination of flags:
Align botRight = AlignBottomRight;
Align botRightBitWise = AlignBottom | AlignRight;
NSLog(@"Are They The Same: %@", (botRightBitWise == botRight) ? @"YES" : @"NO");
//=> Are They The Same: YES
But better, because you can go to-and-fro string values:
NSLog(@"How is that combo aligned? %@", AlignToString(botRightBitWise));
//=> How is that combo aligned? AlignBottomRight
TODO
Version History
v1.2: Jul 4 2017
- [CHANGE] Add explicit
voidto generated function argument list to satisfy Xcode 9’s on-by-default-Wstrict-prototypes. See: https://stackoverflow.com/a/44473380/5260. issue 14 (rentzsch)
v1.1: Mar 25 2014
- [NEW] Add support for hex constants. (Alex Gray)
- [NEW] Add support for very simple bit-shifting constants. (rentzsch)
v1.0.1: May 28 2013
- [FIX] Suppress local unused variable warnings. (maniak-dobrii)
v1.0: Apr 09 2013
- Minor bug fix from 0.2.
v0.2: Dec 10 2012
- [NEW] Generalized to support bidirectional enum label/value lookup and full runtime access to lookup dictionary.
- [NEW] Add passing tests.
- [NEW] Write this README.
v0.1: Dec 9 2012
- [NEW] Devised way to allow split declaration/definition macros to allow use in header/source files.
Prelude: Dec 8 2012
- 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.
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