How to wait for multiple different-timed animations in a generic manner? A reply to http://inessential.com/2013/06/22/technical_notes_on_vespers_full-scree .

TCAppDelegate.m

#import "TCAppDelegate.h"

// Let's use https://github.com/nevyn/SPAsync
#import <SPAsync/SPTask.h>

@interface UIView (SPTaskAnimations)
// Category that returns an abstraction representing an asynchronous operation, rather than just a raw block. We can use this abstraction later to compose multiple of them.
+ (SPTask*)task_animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations;
@end

static UIView *coloredView(UIColor *color, CGPoint position);

@implementation TCAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    
    UIView *red = coloredView([UIColor redColor], CGPointMake(60, 30));
    UIView *gre = coloredView([UIColor greenColor], CGPointMake(20, 200));
    UIView *blu = coloredView([UIColor blueColor], CGPointMake(220, 40));
    [self.window addSubview:red];
    [self.window addSubview:gre];
    [self.window addSubview:blu];
    
    // Let's wait for multiple things to finish.
    [[[SPTask awaitAll:@[
        // Create three different asynchronous operations.
        [UIView task_animateWithDuration:.9 delay:1 options:0 animations:^{
            red.center = CGPointMake(170, 180);
        }],
        [UIView task_animateWithDuration:.4 delay:1 options:0 animations:^{
            gre.center = CGPointMake(120, 220);
        }],
        [UIView task_animateWithDuration:1.5 delay:1 options:0 animations:^{
            blu.center = CGPointMake(220, 220);
        }],
    
    // Add a callback to when all three tasks have finished. Make that callback return yet another thing to wait for (a fade-out)
    ]] chain:^SPTask *(id value) {
        return [UIView task_animateWithDuration:.5 delay:1.5 options:0 animations:^{
            red.alpha = gre.alpha = blu.alpha = 0;
        }];
    // Add a callback to when that one has finished as well.
    } on:dispatch_get_main_queue()] addCallback:^(id value) {
       NSLog(@"All done!");
    }];
    
    // We could have accomplished the same thing by using NSOperation and adding dependencies between them. I'm not sure which one I prefer.
    
    return YES;
}

@end

@implementation UIView (SPTaskAnimations)
+ (SPTask*)task_animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations
{
    SPTaskCompletionSource *source = [SPTaskCompletionSource new];
    [self animateWithDuration:duration delay:delay options:options animations:animations completion:^(BOOL finished) {
        [source completeWithValue:@(finished)];
    }];
    return source.task;
}
@end

static UIView *coloredView(UIColor *color, CGPoint position)
{
    UIView *v = [[UIView alloc] initWithFrame:(CGRect){.origin = position, .size = {20, 20}}];
    v.backgroundColor = color;
    return v;
}

There's probably a need for a "meta"-language to describe a multi-step animation on iOS.