Difference between using and importall

Suppose we want to extend a function called bar in the Foo package. When we do it by using, we need include the package name too:

julia> using Foo
julia> function Foo.bar(...)

But when we do it by importall, we are not required to include the package name:

julia> importall Foo
julia> function bar(...)

When we use importall, function bar(...), and function Foo.bar(...) are equivalent.

This prevents us from accidentally extending a function that we didn't want to extend or didn't know about, and saves us from possibly breaking future implementations of Foo.