Type inference via auto_type

[nguyenhuy]

Having type inference would be helpful in many cases. Details can be found in this great blog post. Let me know what you all think!

P/S: If we decide to introduce this, we need to update our coding guidelines.

[Adlai-Holler]

For the time being, a couple thoughts:

• Using let and var macros inconsistently in a public framework seems unprofessional to me.
• __auto_type can interfere with SourceKit, making development slightly more frustrating.
• __auto_type on its own is ugly but useful in cases like NSMapTable<NSString *, ASDisplayNode *> *mapTable = [self generateMapTable]
• Maybe it would be appropriate to use __auto_type directly but sparingly, in cases where it makes sense, up to the discretion of the coder. NSArray<NSString *> * may not justify it, for example.

[maicki]

I'm sharing the opinion of @Adlai-Holler:

• We should not introduce let and var as it's not common standard
• Using __auto_type can be cumbersome
• We should slowly introduce it in places where it makes sense e.g. for blocks etc.

[nguyenhuy]

Thanks for the thoughtful feedbacks. Let's use __auto_type on a case by case basic and don't introduce project-wise let and var macros. Closing this RFC.