Can't use PromiseKit 2.0 since SGImageCache is requiring 1.5

[xezero]

Error when trying to pod 'PromiseKit', "~> 2.0"

[!] Unable to satisfy the following requirements:

- `PromiseKit/base (~> 1.5)` required by `SGImageCache (2.2.0)`

[xezero]

PromiseKit 2.0 also notably brings the idea of canceling a promise! Seems like it could be useful for SGImageCache if one wants to cancel an image request entirely!? :) A good example would be if we know we're not going to need to retrieve those images anymore, we can free up the slow queue from having to fetch them at some point, since right now the only way to free up the fast queue is to move images to the slow queue.

[staminajim]

The problem here is that PromiseKit 2.0 only works with deployment targets of iOS 8 and higher because it's written in swift, and cocoa pods can only include swift frameworks with iOS 8 targets.

I think this might mean dropping iOS 7 support unless we can figure out a way around that - which would be less than ideal.

[staminajim]

So I had a play around and almost had a way to have an iOS7 only subspec but there's another difficult problem where PMKPromise is objc_subclassing_restricted in PromiseKit 2.0.

SGImageCache is currently relying on being able to subclass that object for the onRetry and onFail blocks.

Maybe if there's a way to implement those using vanilla PMKPromise objects we could make the jump to 2.0.

[xezero]

Hm, my first thought would be to add some category methods and associated objects for the PMKPromise class? A less simplistic (but fun!) alternative could be adding some methods at runtime via class_addMethod.

[staminajim]

Well if there's any way to get a PMKPromise to fire a .then or similar call multiple times then we could fire those onRetry and onFail blocks a different way.

I'm not aware of any way to do that, but I'm also admittedly not overly familiar with advanced promise kit usage. It'd be fantastic if anybody knows a way to do that.