early return + helper

gistfile1.m

- (void)setError:(NSError **)error withOSStatus:(OSStatus)status
{
    if (error != NULL) {
        *error = [NSError errorWithDomain:NSOSStatusErrorDomain code:status userInfo:nil];
    }
}

- (BOOL)play:(NSError **)error;
{
    NSAssert(_graph == NULL, @"Graph is already started");

    OSStatus status;
    
    status = NewAUGraph(&_graph);
    if (status != noErr) {
        [self setError:error withOSStatus:status];
        return NO;
    }        
    
    status = [self addOutputNode];
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = [self addConverterNode];
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = AUGraphConnectNodeInput(_graph, _converterNode, 0, _outputNode, 0);
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = AUGraphOpen(_graph);
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    [self setupDataFormat];
    
    status = [self setDataFormatOfConverterAudioUnit];
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = [self setMaximumFramesPerSlice];
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = [self setRenderCallbackOfConverterNode];
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    status = AUGraphInitialize(_graph);
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    A440SineWaveGeneratorInitWithFrequency(&_sineWaveGenerator, 440.0);
    
    status = AUGraphStart(_graph);
    if (status != noErr) {
        DisposeAUGraph(_graph);
        [self setError:error withOSStatus:status];
        return NO;
    }
    
    return YES;
}