this may fit better in development than first steps, but before I bother the developers, let me ask the basics? would it introduce any ambiguity if Vector{AbstractFloat} was interpreted as Vector{<:AbstractFloat}. The former seems quite natural, and I have been bitten a few times by inadvertently …

Julia’s type parameters are “invariant.” Your suggestion would make them “covariant.” In short: that’s a major design change. One place invariance is crucial is that Julia uses a different memory layout for Vector{Any}, Vector{Union{Int, Missing}} and Vector{Int}, with the latter two being much m…

No, because they are two distinct concepts, and you need a way to express both. This comes up a lot. Probably would make a good blog post to explain the motivation in more detail

thanks. understood. to understand most easily what would be lost by automatic recognition, can someone please give me an example of what call function f(x::Vector{AbstractFloat}); 2; end catches at the moment? regards, /iaw

It catches a Vector{AbstractFloat}, just like it says: julia> x = Vector{AbstractFloat}(5) 5-element Array{AbstractFloat,1}: #undef #undef #undef #undef #undef julia> f(x) 2

thanks. this explains it. I did not realize that an object could be of type AbstractFloat. I thought AbstractFloat was more like an enumeration of possible types of an object, but one that could not be the type of an existing object. julia> x=AbstractFloat(3) 3.0 julia> typeof(x) Float64 This …

[image] iwelch: I did not realize that an object could be of type AbstractFloat. No, an object cannot be of type AbstractFloat, because AbstractFloat is an abstract type — objects can only have concrete types. If you have Vector{AbstractFloat}, each element is a concrete floating-point type,…

yep. this is exactly what I had missed.

if Julia had “compiler warning” settings, it would be good if it emitted a notice [<;warning ;-)) that the use of Vector{...} is much rarer than Vector{<:...} (where … are a couple of common types, like AbstractFloat, Real, etc.). This is probably a common beginner’s error, and would reduce novice…

I have to the conclusion that for beginners, the less type annotations the better. Let the compiler figure things out on its own, and let library writers worry about making sure all of the mathematics on the generic types are sound. See Is a simple, beginner style with named parameters and no unnec…

Ambiguity on Vector{<:Abstract*}?

General Usage

stevengj April 27, 2018, 11:06pm 4

See, for example, this post: Problem with Complex{Rationals} - #7 by stevengj

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Ambiguity on Vector{<:Abstract*}?

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