swift curried functions

Ran across this just now and found the comment by Pavol more interesting than curried functions. Yes Pavol! Totally. This is going to be a recurring problem for a lot of imperative programmers beginning to enter the world of functional programming through Swift. ‘Functional first’ is something I have to continually remind myself of. The original (imperative) gist went something like this:

curried1

Pavol advocates a more functional approach, without the “minutiae” of loops and temp vars:

curried2

Can we continue that train of functional thought? What if we move the separator up the chain, eliminating the function call:

curried3

That was an interim step to see if it worked. Now lets wrap it up and bring back that append function, allowing us to pass any separator:

curried6

Lastly, to make it even more compact, we can remove some syntax noise in the call to reduce:

curried7

Adding Box2D to Xcode

Grab the Box2D folder and drag it into your Xcode project.

b2d1

b2d2

Make sure copy items and the correct target are both checked.

b2d3

In the project build settings, filter by “user”.

b2d4

Under ‘User Header Search Paths’ add a . for the current directory and select recursive.

b2d5

Set ‘Always Search User Paths’ to YES.

b2d6

For the given source file, you need to change the extension to *.mm

b2d7

Doing so, changes the default type to Objective-C++.

b2d8

Finally, import Box2D and begin your journey.

b2d9

CGDataProviderCreateDirect

It’s hard to find an example using CGDataProviderCreateDirect, so here’s a quick snippet:

static unsigned int* data; // used for manipulating pixel data directly

const void * getBytePointerCallback(void *info)
{
	return (void*)data;
}

@implementation SomeView

- (void)createImage
{
    CGDataProviderDirectCallbacks callbacks;
    callbacks.version = 0;
    callbacks.getBytePointer = getBytePointerCallback;
    callbacks.releaseBytePointer = NULL;
    callbacks.getBytesAtPosition = NULL;
    callbacks.releaseInfo = NULL;
    
    float w = self.layer.frame.size.width;
    float h = self.layer.frame.size.height;
    
    w *= [UIScreen mainScreen].scale;
    h *= [UIScreen mainScreen].scale;
    
    int numComponents = 4;
    uint dataLength = w * h * numComponents;
    
    data = malloc(dataLength * sizeof(uint)); // TODO: free
    
    uint r = 255;
    uint g = 0;
    uint b = 0;
    for(int i = 0; i < dataLength; ++i)
    {
        data[i] = 255 << 24 | b << 16 | g << 8 | r;
    }
    
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    
    CGDataProviderRef bitmapProvider = CGDataProviderCreateDirect(data,dataLength,&callbacks);

    CGImageRef bitmap = CGImageCreate(w,
                                      h,
                                      8,    // bits per component
                                      8*numComponents,  // total bits
                                      w*numComponents,  // bytes per row
                                      colorSpace,
                                      kCGBitmapByteOrderDefault,
                                      bitmapProvider,
                                      NULL,
                                      false,
                                      kCGRenderingIntentDefault);    
    
    self.layer.contents = (__bridge id)(bitmap);
    
    CGImageRelease(bitmap);
    CGDataProviderRelease(bitmapProvider);
    CGColorSpaceRelease(colorSpace);
}