数组在Julia中破坏字符串类型 [英] Arrays break string types in Julia

问题描述

以下是设计使然吗?

ASCIIString <: String返回true，但是Array{ASCIIString,1} <: Array{String,1}返回false.

也许这是一个错误，我应该在github上发出拉取请求. (我正在运行v0.4.0-dev + 6210)

Perhaps this is a bug, and I should make a pull request on github. (I'm running v0.4.0-dev+6210)

推荐答案

只需将我的评论转换为答案即可:

just convert my comment into an answer:

您的问题的答案是是".正如julia的文档所述:

the answer to your question is YES. As julia's document says:

用类型论的话来说，朱莉娅的类型参数是不变，而不是协变(甚至是协变).

in the parlance of type theory, Julia’s type parameters are invariant, rather than being covariant (or even contravariant).

在下面的误导性案例中，人们可能会发现

in the misleading case below, one may find that

julia> Int64 <: Int
true

julia> Array{Int64,1} <: Array{Int,1}
true

这是因为Int和Int64是同一类型.

this is because Int and Int64 are the same type.

julia> xdump(Int)
Int64::DataType  <: Signed

julia> xdump(Int64)
Int64::DataType  <: Signed

julia> xdump(Array{Int,1})
Array{Int64,1}::DataType  <: DenseArray{Int64,1}

julia> xdump(Array{Int64,1})
Array{Int64,1}::DataType  <: DenseArray{Int64,1}

我们可以使用typejoin来检查类型A和类型B及其对应的数组"之间的关系.

we can use typejoin to checkout the relationship between type A and type B and their corresponding "arrays".

julia> typejoin(Int64,Int)
Int64

julia> typejoin(Array{Int64,1},Array{Int,1})
Array{Int64,1}

但是

julia> typejoin(ASCIIString,String)
String

julia> typejoin(Array{String,1},Array{ASCIIString,1})
Array{T,N} (constructor with 9 methods)

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