Here is an example of two independent packages colliding when they overload the same method. Package MyPackage Module MyPackage struct MyNumber <: Number value end Base.promote_rule(::Type{MyNumber}, ::Type{S}) where {S<:Number} = MyNumber Base.convert(::Type{MyNumber}, x::…

[image] "Meaning", type-piracy, and method merging julia> YourNumber(5) + MyNumber(3) That can only happen if someone knows the existence of both packages.

[image] "Meaning", type-piracy, and method merging That can only happen if someone knows the existence of both packages. Unfortunately not: I use packages X and Y, not knowing about either MyPackage nor YourPackage, and the authors of X and Y know nothing about each other. X uses MyPackage, Y …

[image] "Meaning", type-piracy, and method merging Unfortunately not: I use packages X and Y, not knowing about either MyPackage nor YourPackage, and the authors of X and Y know nothing about each other. X uses MyPackage, Y uses YourPackage, and I get into trouble. No, then who wrote the YourN…

The problem is that I used X, which has MyPackage as a dependency, as well as Y, which has YourPackage as a dependency. I never cared about MyPackage or YourPackage. I mean, I’m not even trying to add X-outputs and Y-outputs. Already isequal and hash of mixed Any-typed arrays can crash: You cannot …

[image] "Meaning", type-piracy, and method merging The problem is that I used X, which has MyPackage as a dependency, as well as Y, which has YourPackage as a dependency. I never cared about MyPackage or YourPackage. This is still local. The fact that bad promotion code can exist is an entirel…

I do believe there’s an issue here, but it’s separate from the punning/meaning thread so I’ve split it out. Somewhat similar is this bug: https://github.com/JuliaLang/julia/issues/13193

[image] foobar_lv2: Demanding from users that they go up the entire dependency chain is imho unreasonable. This is a good point and one that drove me away from Go[1]. If it’s possible to avoid this sort of thing in Julia, we absolutely should. [1] The issue there is that if any part of your…

Fundamentally this is not an automatically solvable problem: if there are two user-defined number types and no promotion rule for them exists, how can the system possibly know what to do? The only reasonable thing it can do is throw an error. So the only real problem here seems to be that people don…

But the ‘innocent user’ who wants to use both MyPackage and YourPackage without any type of error now has to define methods that resolve the ambiguity/stack overflow, which entails defining methods for functions that are not defined in their code on types that are not defined in their code, i.e., ty…

Optimally, we would not trigger any error at all. Comparison by object identity is a perfectly sensible default. Arithmetic of user-types appearing in hashing is a somewhat temporary clutch to enable fast range hashing and should never throw. Overly general promotion rules, like in the example, are…

Difficulties with promoting numbers

Internals & Design

ChrisRackauckas May 19, 2018, 1:26pm 6

This is still local. The fact that bad promotion code can exist is an entirely separate issue from type-piracy and not really relevant.

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Difficulties with promoting numbers

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