Flag to indicate that the object is immutable

[hughfdjackson]

Flag or function to show that an immutable value is immutable:

Suggestions:

var o = im.object()
o.immutable //= true

Pros:

• simple
• terse

Cons:

• Not unique to immutable objects of this library

var o = im.object()
im.isImmutable(o) //= true

Pros:

• unique to immutable objects of this library (potentially)

Cons:

• Bit clunky

[hughfdjackson]

For the record, .immutable was preferred because it didn't rely on object identity - which can be a tricky situation when you have a system like NPM that will allow the system to use multiple versions of the same library.

If an immutable object is passed back by library N, then querying it via a directly required instance of immutable should work.

[Raynos]

Why do you need this flag?

[hughfdjackson]

To provide a slightly less duck-typy way to deal with mixed immutable and 'regular' objects - for instance, for a deep get that might (not decided yet) include both mutable and immutable objects:

[hughfdjackson]

and, ofc, because npm breaks instanceof as a universal checker - as you demonstrated so amply before with your prototypes problem.

[Raynos]

Functions that deal with mixed immutable and 'regular' objects are very expensive in terms of additional complexity.

Avoid it if you can.

[hughfdjackson]

You may well be right - still undecided on how deep operations should work. That said, sometimes important to know if something's claiming to be (for instance) a promise, or is some other type of return value.

I think this flag will find its place in making it easy to reason about these objects 'in the wild' (when more than one lib exports them). I'll freely admit it's a slight API gamble; but erring slightly more on the side of making it easy for people to integrate into their daily lives doesn't seem like a step too far.

[Raynos]

I prefer x.type === "immutable@Immutable for that kind of stuff, but sure