what is "type piracy"?

[Tamas Papp]

What does the term "type piracy" mean?

The term shows up in julia-related discussions, mostly on
Github. Googling for it leads back these discussions, and a lot of
unrelated stuff about copyright and/or typefaces.

(Apologies if the term is well-known, I am an economist, not a computer
scientist).

[Spencer Russell]

As far as I know "type piracy" is not a widespread term in CS, but has
popped up in the Julia community.

Basically it refers to violations of the Julia guideline that a package
shouldn't define methods of functions it doesn't own on types it doesn't
own.

For example, if package A exports a function `foo`, and package B
defines a type `Bar`, package C shouldn't define `foo(x::Bar)`. It's in
some ways stealing functionality that other packages should be
responsible for, and from a user's perspective it can be confusing if
`using C` changes behavior that's associated with completely different
packages.

-s

[Mike Innes]

Another way to look at this is, redefining a module shouldn't result in method redefinition warnings.