1 * ["a"] # gives error 1 * String[] # returns Vector{Union{}} Why is the second allowed?

[image] sadish-d: But my question is, why is the operation * between an Int64 and a Vector{String} allowed when *(::Int64, ::String) is not defined? * between Int64 and Vector{String} is defined. It will try to broadcast the multiplication across the vector. *(Int64, String) does not exists t…

We can ask Julia which method implements it julia> @which 1 * String[] *(A::Number, B::AbstractArray) @ Base arraymath.jl:21 This makes sense as the idea is c \cdot v for c \in \mathbb k and v a vector would then become a component-wise multiply, useful when you implement your own types. Hop…

I understand that a scalar times a vector is essentially a component-wise multiplication. (I think it calls broadcast?). But my question is, why is the operation * between an Int64 and a Vector{String} allowed when *(::Int64, ::String) is not defined? You can not do, for example, 1 * "a" because *(…

Ok, the type of String[] is getting ignored there. @assert eltype(String[]) == String. I don’t know if I like empty arrays. I tend to use them as default values. I’ll need to rethink them and make sure to treat them as special cases. It turns out that all elements of empty array are true, even when…

Perhaps this topic can help: [image] Behavior of all() and any() on empty vectors General Usage This caught me by surprise: julia> any(x->true, []) false julia> all(x->true, []) true julia> any(x->false, []) false julia> all(x->false, []) true This seems like a bug -…

Thanks, @Sukera . I had no doubt that people had put thought into the choice of behavior. But things are not any clearer to me. (And maybe that’s okay.) I suppose all programming languages have to deal with empty sets/arrays. There are two things that confuse me. Why all and any and the like work …

[image] sadish-d: Why all and any and the like work on non-Boolean arrays at all. Probably for the same reason that 'a' + 1 == 'b' and 1 == true. They only work in the empty case, because the empty case doesn’t care about the type; there is no logical predicate you can write that will make th…

The simplest mental model here is that any is true if there’s at least one true and all is false if there’s at least one false. Array element types don’t matter; it’s the values that do. In fact: julia> all([false, "no errors!"]) false julia> any([true, "no errors!"]) true

any(f, vec) is asking the question “of all the elements in vec, is there one that fulfills the predicate f?” I like the framing as a mnemonic: any(f, vec): There is an element in vec that fulfills the predicate f. all(f, vec): There is no element in vec that fails to fulfill the predicate f. B…

Why does `1 * String[]` return a Vector{Union{}}?

New to Julia

Sukera October 17, 2023, 2:30pm 6

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Why does `1 * String[]` return a Vector{Union{}}?

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