Question

Are there any disadvantages, if I were to replace all my accessors (get-like const methods) with readonly properties in Objective-C? Are they interchangeable?

I prefer readonly properties for documentation/readability.

Coming from C++, I am thinking of replacing all my const methods (non-mutable methods) with readonly properties in ObjC.

If I adhere to this convention, then I can automatically assume that any regular methods will be changing state (non-const method in C++). Also from a functional-programming perspective, knowing that a readonly property won’t change any state (having no side-effects) is useful.

Answer 1

Yes, they are interchangable.

@interface MyClass : NSObject
@property (nonatomic, readonly) NSString *myStr;
@end

is the same as

@interface MyClass : NSObject
-(NSString *)myStr;
@end
@interface MyClass() { NSString *_myStr } 
@end
@implementation MyClass
-(NSString *)myStr { return _myStr; }
@end

Although you won’t see it in your code, a property does create a myStr method that is accessible. In both cases, you could use
self.myStr or [self myStr] to invoke the method.

Side note: if you are using iOS 6 you do not need to include the @synthesize statement. Otherwise you would write: @synthesize myStr = _myStr; in the implementation file.