BREAKING: Alias merge as concat for Set and Map collections

[leebyron]

These methods are extremely similar, but have differing implementations with different performance characteristics. This makes concat an alias of merge, sharing the implementation for those methods.

[randallb]

I upgraded to RC9 and at runtime, orderedMaps can't concat. Concat returns as undefined. Working on a test case now.

[randallb]

Given a package.json:

{
  "name": "immmutable-bug-simple",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "immutable": "^4.0.0-rc.9"
  }
}

and an index.js of

const immutable = require('immutable');

const orderedMap = immutable.OrderedMap();
const orderedMap2 = immutable.OrderedMap();
orderedMap.concat(orderedMap2)

I get:

TypeError: orderedMap.concat is not a function
    at Object.<anonymous> (/Users/rb/code/experiment/immmutable-bug-simple/index.js:5:12)

[randallb]

Working to see if I can help write code to fix.

[randallb]

Opening a new issue too.