Proposal for SharedFunctions.jl package for optional dependency management

Internals & Design
28

This is true although I am not sure how to be more clear. A different generic function with the same name is a function with the same name as another function… For example:

module A
f(x) = x
end

module B
f(x, y) = x + y
end

Here A.f and B.f are different (generic) functions.

The reason why we cannot just merge the two f is because of how you write generic code. An example of a generic function is push!. We can see the docs for it:

  push!(collection, items...) -> collection


  Insert one or more items at the end of collection.

We now know what the generic function Base.push! means. We can extend that function to our own types by adding a method to Base.push!. Everyone who extends this function agrees that they are using the documented meaning of push!. We can now make a generic function that takes a collection and uses the function Base.push! somewhere in the function body, on that collection.

Now, let’s consider another function with the same name:

module MyGame

"""
    push!(p)
Push the person `p` to an adjacent square
"""
function push!(p) end

end

This has a completely different meaning than Base.push!. This is fine though because in generic code we either use Base.push! or MyGame.push!. These are different functions so we need the concept of namespaces to decide which one to use.

Now, if Base.push! and MyGame.push! was merged, it is impossible to look at a piece of generic code that uses push! and figure out what it is doing. Is it adding things to a collection or pushing person’s around? As already been said, all functions are generic, so without a way to know what the generic functions do, it is impossible to reason about generic code. Any function could mean anything.

Therefore, with regards to the proposed SharedFunctions, it can either be that

  1. The first one to claim a function name gets to document it. We then know what that function does and can write generic code with it.
  2. Everyone extends the function with the same name with no regards of what the function means. It is then not possible to write generic code with that function (because the concept of the meaning of a function doesn’t exist anymore).
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