[英]Get parameters of a parametric type
Suppose I define a type like that 假设我定义了类似的类型
type Point{Tx, Ty} end
Then I create a variable of this type, for example, 然后我创建一个这种类型的变量,例如,
a = Point{Int64, :something}()
Now, I only know that I can get the type of a
by typeof(a)
. 现在,我只知道我能得到的类型,
a
由typeof(a)
。 That is, Point{Int64, :something}
. 也就是说,
Point{Int64, :something}
。 But, what I need is just the parameters Tx
and Ty
. 但是,我需要的只是参数
Tx
和Ty
。
Are there ways that I can get those parameters Tx
and Ty
? 我有办法获得这些参数
Tx
和Ty
吗?
You can define a function as follows 您可以按如下方式定义函数
eltypes{Tx,Ty}(::Type{Point{Tx, Ty}}) = (Tx, Ty)
eltypes(p) = eltypes(typeof(p))
(here ::Type{Point{Tx, Ty}}
matches an argument of type Point{Tx, Ty}
) and use it (此处
::Type{Point{Tx, Ty}}
匹配Point{Tx, Ty}
类型的参数并使用它
julia> eltypes(Point{Int, Float64}())
(Int64,Float64)
This is a frequently used idiom, for example in Base there is the similar function 这是一种常用的习语,例如在Base中有类似的功能
eltype{T}(::Type{Set{T}}) = T
eltype(x) = eltype(typeof(x))
typeof(a)
is a DataType
which has many fields. typeof(a)
是一个包含许多字段的DataType
。 you can get those names via: 你可以通过以下方式获得这些
julia> fieldnames(DataType)
10-element Array{Symbol,1}:
:name
:super
:parameters
:types
:instance
:size
:abstract
:mutable
:pointerfree
:ninitialized
so if you need those parameters, run 所以,如果您需要这些参数,请运行
julia> collect(typeof(a).parameters)
2-element Array{Any,1}:
Int64
:something
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.