MirrorKit

Inspired by Swift's MirrorType and MAObjcRuntime, this framework aims to simplify working with the Objective-C runtime and offer a simple way to reflect classes and objects.

Installation

MirrorKit is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "MirrorKit"

Usage

Documentation for MirrorKit is on Cocoadocs.

#import "MirrorKit.h"
...

XZYObject *foo = [[XZYObject alloc] initWithBar:bar];
MKMirror *reflection = [MKMirror reflect:foo]; // works for classes too

// Get a list of foo's properties, retrieve information about a property
NSArray *properties = reflection.properties;
MKProperty *property = properties.firstObject;
NSString *propertyName = property.name;
BOOL readwrite = !property.isReadOnly;

// Discover all loaded subclasses of any class!
NSArray *subclasses = [NSDictionary allSubclasses];
NSLog(subclasses); // 20+ classes... wow

Here's where the real fun begins. Let's create a class at runtime:

// Start here by naming it. Your class will implicitly inherit from NSObject.
MKClassBuilder *builder = [MKClassBuilder allocateClass:@"NSAtom"];

// Create and add IVars...
MKIVarBuilder *nameIvar name:@"_name" size:sizeof(id) alignment:log2(sizeof(id)) typeEncoding:@(@encode(id))];
MKIVarBuilder *lengthIvar = [MKIVarBuilder name:@"_length" size:sizeof(NSUInteger) alignment:log2(sizeof(NSUInteger)) typeEncoding:@(@encode(NSUInteger))];
[builder addIVars:@[nameIvar, lengthIvar]];

// Create some methods...
NSString *initTypes  = [NSString stringWithFormat:@"%s%s%s", @encode(id), @encode(id), @encode(SEL)];
NSString *fooTypes   = [NSString stringWithFormat:@"%s%s%s%s", @encode(void), @encode(id), @encode(SEL), @encode(id)];
MKSimpleMethod *init = [MKSimpleMethod
    buildMethodNamed:@"init"
    withTypes:initTypes
    implementation:imp_implementationWithBlock(^(id self) {
        self = [super init];
        if (self) {
            NSUInteger len = 5;
            [self setIVarByName:lengthIvar.name value:&len size:sizeof(len)];
            [self setIVarByName:nameIvar.name object:@"NSExceptional"];
            NSLog(@"Called init");
        }
        return self;
    }
)];

MKSimpleMethod *fooMethod = [MKSimpleMethod
    buildMethodNamed:@"foo:"
    withTypes:fooTypes
    implementation:imp_implementationWithBlock(^(id self, id someObject) {
        NSLog(@"-[%@ foo:] %lu: %@",
            NSStringFromClass([self class]),
            [self length],
            [self name], 
            [someObject description]
        );
    }
)];

// Create some property attributes, using either MKMutablePropertyAttributes or a dictionary to create an MKPropertyAttributes object
MKMutablePropertyAttributes *nameAttributes = [MKMutablePropertyAttributes attributes];
nameAttributes.isReadOnly  = YES;
nameAttributes.backingIVar = nameIvar.name;
[nameAttributes setTypeEncodingChar:MKTypeEncodingObjcObject];
NSDictionary *lengthAttributesDict = @{
    MKPropertyAttributeKeyNonAtomic:       @YES,
    MKPropertyAttributeKeyTypeEncoding:    [NSString stringWithFormat:@"%c", (char)MKTypeEncodingUnsignedLongLong],
    MKPropertyAttributeKeyBackingIVarName: lengthIvar.name
};
MKPropertyAttributes *lengthAttributes = [MKPropertyAttributes attributesFromDictionary:lengthAttributesDict];

// Initialize some properties with those attributes...
MKProperty *nameProperty   = [MKProperty propertyWithName:@"name" attributes:nameAttributes];
MKProperty *lengthProperty = [MKProperty propertyWithName:@"length" attributes:lengthAttributes];
// Properties need getters and setters! These aren't too straightforward, sadly.
// Casting is necessary. These macros make it kinda simple.
MKSimpleMethod *getName   = MKPropertyGetter(pName, id __strong);
MKSimpleMethod *getLength = MKPropertyGetter(pLength, NSUInteger);
MKSimpleMethod *setLength = MKPropertySetter(pLength, NSUInteger);

// Add the methods, and properties
[builder addMethods:@[init, fooMethod, getName, getLength, setLength]];
[builder addProperties:@[nameProperty, lengthProperty]];

// Register the class and create an instance of it!
Class myClass = [builder registerClass];
id myAtom     = [myClass new];

To-do

• Finish testing
• Add OS X demo

Author

Tanner Bennett, tannerbennett@me.com

License

MirrorKit is available under the MIT license. See the LICENSE file for more info.