const reducers

[2ZeroSix]

Allow to build entire reducers tree as const object.

• add CombinedReducer class to easily combine reducers in const context
• mark TypedReducer constructor as const
• add UntypedReducer as shorthand for TypedReducer<State, dynamic>.
• add related tests
• add related docs in code and doc/combine_reducers.dart

[codecov-io]

Codecov Report

Merging #73 (4da85ce) into master (8872c0b) will decrease coverage by 3.21%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
- Coverage   92.10%   88.88%   -3.22%     
==========================================
  Files           2        2              
  Lines          38       45       +7     
==========================================
+ Hits           35       40       +5     
- Misses          3        5       +2     

Impacted Files	Coverage Δ
lib/src/utils.dart	90.00% <75.00%> (-10.00%)	⬇️

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[hacker1024]

I think similar changes can also be made to middleware.

[hacker1024]

This PR has been open for a while, does anyone have anything to say?

[brianegan]

Thanks! Sorry -- only have a little bit of time for open source these days and missed this one. Could you please describe in a
bit more detail the problem you want to solve with this PR? Sure, const is nice, but this PR seems to introduce some complexity in order to support const Reducers. For example, combineReducers and CombineReducers looks kinda rough.

Do const reducers bring enough of an advantage to outweigh the larger API surface?

In my view, Reducer classes are instantiated once, when the app is first created. They aren't like Widgets which can re-instantiated over and over, where a const constructor really shines. What do you think?