Faking Protected Methods in Objective-C

protectedMethods.m

//
//  main.m
//  Protected
//
//  Created by Benedict Cohen on 07/03/2012.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//
//
// Unlike other object orientated languages Objective-C does not 
// provide a mechanism for scoping methods as public, protected or private. 
// In Objective-C all methods are essentially public. Private methods can be 
// faked by declaring the methods within an anonymous @interface within the 
// implementation file (i.e. the .m file).
//
// That only leaves protected methods. The common practice is to simply make 
// a note in the documentation or in a comment that a method should be treated 
// as protected. This approach isn't ideal because:
// - Not everyone reads the comments/documentation
// - Code can change and the comments/documentation not updated
//
// The following is a macro that allows protected methods to be annotated in 
// the code. It's incredibly simple. It works by appending a string to the end 
// of the method name. It also works with properties too. The intend is not to 
// enforce method scope but to indicate the indent of a method.




/*************************************
 
 The macro

 This is the macro that does the magic. It's stupidly simple
 The string is append not prepended so that setters remain sane 
 *************************************/

#ifndef PROTECTED
#define PROTECTED(methodName) methodName ## _protected
#endif




/*************************************
 
 BaseClass

 This is the base class that has some protected methods 
 *************************************/

#import <Foundation/Foundation.h>


@interface BaseClass : NSObject
//a protected method. Note that the colon is outside of the macro.
-(void)PROTECTED(aProtectedMethod):(id)withAnArgument;

//a protected property.
@property(readwrite, nonatomic, strong) NSString * PROTECTED(aName);
@end


@implementation BaseClass
//implmenting a protected method
-(void)PROTECTED(aProtectedMethod):(id)withAnArgument
{
    NSLog(@"%@ - %@", [self className], NSStringFromSelector(_cmd));
}

//implementing a protected property. Note that we are still specifing the name of the ivar to use to the property.
@synthesize PROTECTED(aName) = _aName;

@end




/*************************************
 
 SubClass

 This is the subclass which will access the protected methods 
 *************************************/

@interface SubClass : BaseClass
//Nothing special about these declarations
-(void)callSuperProtected;

//this is simple exposing supers protected method
@property(readonly) NSString *aName;
@end


@implementation SubClass

-(void)callSuperProtected
{
    //Calling a protected method on super. Again, note that the colon is outside of the macro.
    [super PROTECTED(aProtectedMethod):nil];
}

-(NSString *)aName
{
    //It works with dot syntax too! (OK, this does look weird).
    return super.PROTECTED(aName);
}
@end




/*************************************
 
 Other calling examples
 
 *************************************/

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        //This line will not compile due to a 'method not found' error
        //[[BaseClass new] aProtectedMethod:nil];
        
        //Code-completion will still suggest the protected methods but they will be 
        //displayed as 'aProtectedMethod_protected:' so it's clear what there purpose is.
        //This line will compile
        [[BaseClass new] aProtectedMethod_protected:nil];
        
        //This line will compile
        [[SubClass new] callSuperProtected];        
    }
    
    return 0;
}