茱莉亚的代表团是什么? [英] What is delegation in julia?

问题描述

我经常看到对授权的引用， 或Julia中的委托设计模式.

I see occational references to delegation, or the delegation design pattern in Julia.

这是什么?

例如我在

• DataStructures.jl中的此文件

推荐答案

这是通过合成(而不是继承)实现的多态形式

This is a form of polymorphism via composition (rather than inheritance)

说一个具有包装器类型的包装器，包装了一个具体子类型AbstractT的实例 包装器本身应为AbstractT的子类型 (并非nesc总是正确的，而是总的来说.)

Say one has a wrapper type, wrapping some instance of a concrete subtype of AbstractT where the wrapper itself is intended to be a subtype of AbstractT (Not nesc always true, but in general).

要添加所有精确的子方法，例如AbstractT的子类型， 我们想委托这些方法中的某些或全部到包装的对象. 我们通过元编程来做到这一点. 如何执行此操作有一些变体. 但是总的来说，提取是很难的模式，因此人们经常自己编写.

To add all the methods one exacts such a subtype of AbstractT to have, we want to delegate some or all of those methods to the wrapped object. We do this via metaprogramming. There are a few varients on how to do this. But in general it is a hard pattern to abstract so people often write their own.

说所有AbstractT子类型都应实现 1arg length，size和mean

Say that that all AbstractT subtypes should implement 1arg length, size and mean

struct WrappedT{T<:AbstractT} <: AbstractT
    backing ::T
    ...
end

for fun in (:(Base.length), :(Base.size), :(Statistics.mean))
    @eval ($fun)(x::WrappedT, args...) = ($fun(x.backing, args...))
end

通常，您不会委派所有方法，因为有些方法您想做不同的事情，那就是最终创建新类型的关键所在.

Generally you won't delegate all the methods, since some you will want to do differently, that is the point of creating the new type after all.

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