类型定义:期望的 UnionAll，得到 TypeVar [英] Type definition: expected UnionAll, got TypeVar

问题描述

在 v0.6 的 Julia 手册中，我发现以下内容:

In the Julia manual for v0.6 I find the following:

abstract type Pointy{T} end
struct Point{T} <: Pointy{T}
    x::T
    y::T
end

这很好用，我认为以下内容也应该:

This works fine, and I thought the following should as well:

abstract type Foo{V, F} end
struct Bar{V, F} <: Foo{V, F}
    x::V{F}
end

Bar 的定义却给出了以下错误

The definition of Bar gives, however, the following error

ERROR: TypeError: Type{...} expression: expected UnionAll, got TypeVar

出了什么问题，我怎样才能实现我真正想要的，即指定 V<:AbstractVector 和 F<:AbstractFloat?

What is wrong, and how can I achieve what I really want, namely to specify that V<:AbstractVector and F<:AbstractFloat?

推荐答案

试试这个:

julia> abstract type Foo{T} end

julia> struct Bar{T<:AbstractFloat,V<:AbstractVector{T}} <: Foo{T}
           x::V
       end

julia> Bar{T}(v::AbstractVector{T}) = Bar{T,typeof(v)}(v) # constructor
Bar

julia> Bar(rand(3))
Bar{Float64,Array{Float64,1}}([0.387467, 0.535419, 0.240748])

julia> Bar(rand(Int, 3))
ERROR: TypeError: Bar: in T, expected T<:AbstractFloat, got Type{Int64}
Stacktrace:
 [1] Bar(::Array{Int64,1}) at ./REPL[4]:1

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