function Base.+ must be explicitly imported to be extended

Question

i'm pretty new to julia forgive me if my question is dumb,

for exmaple i defined a type like this:

type Vector2D
    x::Float64
    y::Float64
end

and 2 object w and v:

v = Vector2D(3, 4)
w = Vector2D(5, 6)

if i add them up it will raise this err : MethodError: no method matching +(::Vector2D, ::Vector2D) it's ok , but when i want to define a method for summing theses object

+(a::Vector2D, b::Vector2D) = Vector2D(a.x+b.x, a.y+b.y)

it raise this error :

error in method definition: function Base.+ must be explicitly imported to be extended

julia version 0.5

score 11 · Accepted Answer · answered Mar 19 '17 at 16:41

11

As the error message says, you must tell Julia that you want to extend the + function from Base (the standard library):

import Base: +, -

+(a::Vector2D, b::Vector2D) = Vector2D(a.x + b.x, a.y + b.y)
-(a::Vector2D, b::Vector2D) = Vector2D(a.x - b.x, a.y - b.y)

answered Mar 19 '17 at 16:41

David P. Sanders

5,210
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5

Or just `Base.+(a::Vector2D, b::Vector2D) = Vector2D(a.x + b.x, a.y + b.y)` – Chris Rackauckas Mar 19 '17 at 16:51
7

Note that in Julia 0.6, this becomes `Base.:+`. – David P. Sanders Mar 19 '17 at 17:40
@DavidP.Sanders what's the reasoning behind that? (or do you have a link to a discussion about the relevant change?) – Alexander Morley Mar 19 '17 at 19:47
I think it's due to the new broadcasting functionality with `.`; see e.g. http://julialang.org/blog/2017/01/moredots – David P. Sanders Mar 19 '17 at 20:03

function Base.+ must be explicitly imported to be extended

1 Answers1