Proper Way to overload operators


#1

Hello,

I have been recently using julia and I want to know what the “proper” way of overloading operators is.

Right now whwat I’m doing is defining a module and, inside that module i have basically the following:

module mymodule
import Base : +,-,*,/ .....
.....
export +,-,*,/

struct MyStruct
end

function +(x::MyStruct, y::MyStruct)
...
end

.....
end

And then for each operator I want to define in addition to implementing the method I have to remember to modify what I import and export from my module.

Is there a cleaner way to do this?


#2

Just do

function Base.:+(x::MyStruct, y::MyStruct)
    ...
end

No import or export required. (export is not required in any case, because Base exports are already visible to any caller.) This idiom has the added benefit that it is clear at the function-definition site that you are modifying a Base function.

Note that it is Base.:+, note Base.+, to distinguish it from a call Base .+ (...) to .+.


#3

Hi,

This seems much more sensible, thanks!

Quick question though, what does the : do at Base.:+ exactly? I understand that it is to disambiguate from a call to the broadcasted + but how does it prevent it? Is the + function actually defined in Base as :+?


#4

: is used to “quote” symbols after ., it is part of the syntax (cf quoting for symbols, eg :a, :b). It is not necessary, but you could quote eg

julia> Base.:sum
sum (generic function with 13 methods)