Function must be explicitly imported to be extended

[dpo]

A discussion over at Docile.jl exposed the following behavior with Julia 0.3 and certain builds of Julia 0.4:

julia> methods(factorize)  # Output omitted
julia> factorize(a, b, c, d, e) = ()
ERROR: error in method definition: function LinAlg.factorize must be explicitly imported to be extended

while other builds of Julia 0.4 give:

julia> methods(factorize)  # Output omitted
julia> factorize(a, b, c, d, e) = ()
factorize (generic function with 8 methods)

It seems like one should be able to define a function with the same name as a function in Base, but which isn't mean to extend it. Or is this behavior intentional somehow?

[ihnorton]

I'm pretty sure this is intentional at this point. See also #2327 #8283.

[JeffBezanson]

The error seems to have gone away. I have no idea how that happened.

[dpo]

Are you expecting an error to be raised or not?

[JeffBezanson]

There should be an error.

[JeffBezanson]

My commit a3d637f is at fault.

[JeffBezanson]

Also, to clarify, you can define a new function with the same name as one in Base, but not when that name from Base has already been used to refer to the Base function.

[dpo]

That makes a lot of sense. And calling methods() would qualify as referring to the Base function I suppose?!

[JeffBezanson]

It's not the call to methods but the use of the factorize identifier.

[MichaelHatherly]

Thanks for the clarification Jeff.