isCopyable and isAssignable

[James Buren via Digitalmars-d-learn]

On Sunday, 9 October 2016 at 07:23:05 UTC, Nordlöw wrote:
> Now that we have isCopyable from
>
> https://github.com/dlang/phobos/pull/4706
>
> can somebody briefly outline when something fulfills 
> `isCopyable` but not `isAssignable` and vice versa?

I would imagine that an intermediate value, or other lvalue, may 
be copyable, but not assignable.