The meaning of “meaning” A common theme that comes up when discussing type-piracy/method merging, etc. is that there “can only be one meaning” for a given function without namespace qualifications (I am being careful there to say function, not method). I just want to get some clarification from th…

[image] rdeits: Just to show that we’re not kidding around about type piracy being a bad idea, I need no convincing! Your precise definition of type piracy was enough for me, and I find it hard to think of examples where it would be a good idea. That said, it also seems like it is unlikely…

[image] ChrisRackauckas: That can only happen if someone knows the existence of both packages. Agreed, it is a really neat example, but I also think it may be more instructive as an example of why broad conversions and promotions with abstract base types are dangerous (as I am pretty sure it …

[image] jlperla: And (in cases where it is not type-piracy) what is wrong with punning on disjoint sets of types? It can be an issue with readability. The problem that I’ve seen in practice, is that if you are looking at a piece of generic code, and you see: a * b ^ c, you have zero idea wh…

I don’t think punning is bad, who is to say the Base is the right term and anything else a pun? I also think that methods should be allowed to merge , reduce can mean related but different things defined in different modules , which have no interest in extending each other because they are unaware …

[image] TsurHerman: I don’t think punning is bad, who is to say the Base is the right term and anything else a pun? I don’t think that’s what people have been saying. My understanding is that punning is really bad when a name has different meanings in the same namespace. It’s not a problem …

Here is an example, I just ran into. It seems to me that this is type piracy, and I should avoid it by defining a new method that is local to my module: import Base.* *(A::Vector{T}, b::SVector{N,T}) where {T,N} = [ a * b for a in A ] this arose because I have a complex assembly of a vector of SVe…

Yes, that is indeed type-piracy. You are extending a method that you haven’t locally defined to take arguments where none of the argument types are locally defined. All of a sudden [1,2,3] * @SVector [1,2,3] will no longer throw an error. You can either create a new function, or wrap one of the inp…

Great, thank you - I guess the wrapping is the key point here. In my case I can just define a new function, but if I wanted to use somebody else’s module in this way, then I would need to wrap my input to make it clear which version of * I am using with affecting anybody else. Makes perfect sense.

[image] TsurHerman: When you are adding a method to a module , you immediately invalidate the binary cache for that module. This is not true. Methods don’t belong to modules: there’s just one global method table, and all of them are in there. Also, the compiler keeps track of exactly what ana…

"Meaning", type-piracy, and method merging

Internals & Design

TsurHerman May 20, 2018, 2:01pm 21

Agreed

Difficulties with promoting numbers

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"Meaning", type-piracy, and method merging

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