为什么以下类型声明 and/or 实例化在 Julia 1.0 中不起作用？

Question

我有圈型

struct Circle{T <: Real}
  # radius is a subtype of
  # the real number approximation types
  R::T
  # The center is a named pair of real
  # number approximation types
  C::NamedTuple{T, T}
end

我想实例化

circles = NamedTuple(
    A = Circle(1, ( 1,  1)),
    B = Circle(1, ( 2,  2))
  )

产生错误

ERROR: LoadError: MethodError: no method matching Circle(::Int64, ::Tuple{Int64,Int64})
Closest candidates are:
  Circle(::T<:Real, ::NamedTuple{T<:Real,T<:Real}) where T<:Real

为什么会出现这个错误，我做错了什么？

Answer 1

Named tuples 由名称和元组参数化：

julia> struct Circle{T <: Real}
         R::T
         C::NamedTuple
         Circle(r::T, c::NamedTuple{N,Tuple{T,T}}) where {N, T <: Real} = new{T}(r,c)
       end

julia> Circle(1, (a=1, b=2))
Circle{Int64}(1, (a = 1, b = 2))

如果要用元组构造Circle，可以提供默认映射：

julia> function Circle(r::T, c::Tuple{T,T}) where {T <: Real}
           a, b = c
           return Circle(r, (a=a, b=b))
       end
Circle

julia> Circle(1, (1, 2))
Circle{Int64}(1, (a = 1, b = 2))

如果不需要命名元组，可以使用常规元组：

julia> struct Circle{T <: Real}
         R::T
         C::Tuple{T, T}
       end

julia> Circle(1, (1, 2))
Circle{Int64}(1, (1, 2))

为什么以下类型声明 and/or 实例化在 Julia 1.0 中不起作用？

Why is the following type declaration and/or instatiation not working in Julia 1.0?

types

type-conversion

julia

type-constructor