merge should return the same object when no meaningful changes were applied

[raorao]

I think it would be helpful if merge returned the same object when no changes were made. Here's what I mean:

obj  = Immutable({ key: 'value' })
obj1 = obj.merge({ key: 'new value '}) 
obj2 = obj.merge({ key: 'value' }) //no meaningful change

// current behavior
obj === obj1 //false
obj === obj2 //false

// ideal behavior
obj === obj1 //false
obj === obj2 //true

Immutable.js provides this feature with their 'set' function, which I've found helpful in the past.

This allows users to run quick checks to see if anything has changed after a merge, which would, for instance, be useful in the context of react/flux. While the check can be done after the fact (using a deepEquals function or something like that), combining that logic with merge has obvious performance benefits.

Maybe both versions of merge should be included in the public API, e.g. 'merge' and 'safeMerge' -- but that may also be overkill. Interested to hear thoughts on this.

[rtfeldman]

Oh nice! I think this should be a very inexpensive check to do...I'll take a crack at it real quick.

[rtfeldman]

Changed in c7887bb