Scala: Why mapValues produces a view and is there any stable alternatives?

There’s a ticket about this, SI-4776 (by YT).

The commit that introduces it has this to say:

Following a suggestion of jrudolph, made filterKeys and mapValues
transform abstract maps, and duplicated functionality for immutable
maps. Moved transform and filterNot from immutable to general maps.
Review by phaller.

I have not been able to find the original suggestion by jrudolph, but I assume it was done to make mapValues more efficient. Give the question, that may come as a surprise, but mapValues is more efficient if you are not likely to iterate over the values more than once.

As a work-around, one can do mapValues(...).view.force to produce a new Map.