Map returns an Immutable object

I don’t really understand why .map is wrapped to return an Immutable object. This seems needlessly restricting. In combination with #16, this also causes unexpected stack overflow errors.

Immutable([1,2,3]).map(function() {
   return React.createElement( "div", null );
});
// too much recursion

[rtfeldman]

map does indeed return a collection of elements which may be completely unrelated to the original elements. However, map is still supposed to return the same type of collection you began with. If you call [].map you get back an Array, if you call $().map you get back a jQuery object, and if you call Immutable([]).map, you get back a seamless-immutable array. This is the standard map behavior.

I sympathize with the fact that this map implementation doesn’t work with React components, because I use seamless-immutable with React and find it annoying that this doesn’t Just Work. I manage this annoyance by using _.map when it finally comes time to turn my seamless-immutable arrays into React components, but naturally it would be less trouble in this particular use case if I didn’t have to.

That said, I don’t think it makes sense to couple this library to React, and I don’t see a strong case for changing map on its own merits. When libraries start developing implicit dependencies on other libraries, unexpected consequences tend to snowball into unpleasant surprises. I value the simplicity and consistency of this library, and hope to maintain it.

As such, I appreciate your perspective, but the current design still makes the most sense to me overall. 😃

[rtfeldman]

This is by design. One of the invariants of the library is that once you invoke Immutable, what you get back is immutable, and continuing to use its methods will only yield further immutable results.

However, since you can pass seamless-immutable’s data structures to other JS libraries, if you really want a mutable copy back, you can just pass them to other libraries that are not designed for immutability.

For example:

_.map(Immutable([1,2,3]), function() {
   return React.createElement( "div", null );
});
// no error