Side-effect free containers for E

[Tyler Close]

> makes is compelling.  The problem is not created simply by
> the existence of
> mutable containers.  I pushed us over the cliff when I
> designed the mutable
> and immutable containers to share so much protocol, and
> therefore, to be so
> interchangeable with each other.  As a result, if a mutable
> container is
> accidentally used where an immutable one should have been
> used, the program
> will often still work under benign and common conditions --
> as when neither
> side mutates the container.

You also made the same mistake when you decided to make sets the same
type as maps. I've found that I often design services where I let
client code choose which capability to use in performing the service
by exposing the keys in a (key => cap) map. If I forget to mask off
the values before passing out the container, I would leak all the
caps.

Tyler


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