Question

I’ve got the following code:

#import <Foundation/Foundation.h>
#import "Game.h"

@interface World : NSObject

@property (nonatomic, strong) Game *game;

+(id)sharedInstance;

//---------------------------------------

#import "World.h"

@implementation World

@synthesize game = _game;

+(id)sharedInstance {
    DEFINE_SHARED_INSTANCE_USING_BLOCK(^{
    return [[self alloc] init];
});
}

Yet when I try to set the game property:

-(id)initWithLevelIdentifier:(int)identifier {
    if (self = [super init]) {
        self.currentLevel = [[Level alloc] initWithIdentifier:identifier];
        // stuff

        [[World sharedInstance] setGame:self];
    }

    return self;
}

I get:
“Cannot initialize a parameter of type ‘int *’ with an lvalue of type ‘Game *__strong'”

Why does it think this is an int *, when it’s clearly specified as a Game type?

Answer 1

You have a circular dependency here. I’m betting Game.h also imports World.h. See @class vs. #import in header compile time saving with Clang?.

The solution is to just note in World.h that Game is a class, but not import the header:

#import <Foundation/Foundation.h>

@class Game;    // <=== rather than #import

@interface World : NSObject

@property (nonatomic, strong) Game *game;

+(id)sharedInstance;

---

Note that your code here has a design problem as well. The mere act of creating a Game object changes the current World game. This means that it is very difficult to treat Game as a non-singleton (just creating it modifies global state), yet Game is not a singleton. This is very surprising behavior in an initialization method. It would be better to move the setGame: call outside of init and let the caller decide whether this is now the global current game. It would be reasonable to put this in World as -[World createNewGame].