Add backward compatible Obj-C Generic support for Tasks.

[nlutsenko]

This support latest syntax in Xcode 7, and also is backward compatible via macro.
cc @grantland, @hallucinogen, @richardjrossiii

[grantland]

LGTM

[grantland]

Do we not have to update the implementation files?

[nlutsenko]

Aha, I am glad you asked - the answer is actually no, ObjC generics are only for interfaces/APIs and enforce replacement with id when used inside implementation (it resolves into a compiler error if used inside the implementation)

[grantland]

lol nice

[nlutsenko]

I've just updated the PR, so we have covariant support on this.
This is to enable something like this:

BFTask<NSString *> *stringTask = [BFTask taskWithResult:[NSString string]];
BFTask<NSMutableString *> *mutableStringTask = [BFTask taskWithResult:[NSMutableString string]];
stringTask = mutableStringTask; // This is valid, since NSMutableString is a subclass of NSString

[richardjrossiii]

<3 covariants.

On Sep 2, 2015, at 8:07 PM, Nikita Lutsenko [email protected] wrote:

I've just updated the PR, so we have covariant support on this.
This is to enable something like this:

BFTask<NSString *> *stringTask = [BFTask taskWithResult:[NSString string]];
BFTask<NSMutableString *> *mutableStringTask = [BFTask taskWithResult:[NSMutableString string]];
stringTask = mutableStringTask; // This is valid, since NSMutableString is a subclass of NSString
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[grantland]

even better!

[facebook-github-bot]

@nlutsenko updated the pull request.