get_in用于嵌套列表& lix剂中的结构 [英] get_in for nested list & struct in elixir

问题描述

我有一个结构

s = [
  a: %Bla{
   b: "c"
  }
]

我想参加 c 的价值。我正在尝试

I want to take c value from it. I'm trying to do

get_in(s, [:a, :b])

但这并不是为了从结构中获取价值。有没有类似的方法可以让我从带有嵌套结构的列表中获取 c ？

But it's not designed to take value from the struct. Is there any analogue which allows me to fetch c from the list with nested struct?

推荐答案

已记录， get_in 默认情况下不适用于结构：

As documented, get_in does not work with structs by default:

Access语法（foo [bar]）不能用于访问结构中的字段，因为结构默认情况下不实现访问行为。这也是设计决策：动态访问查找旨在用于动态键值结构（如地图和关键字），而不用于静态结构（如结构）。

The Access syntax (foo[bar]) cannot be used to access fields in structs, since structs do not implement the Access behaviour by default. It is also design decision: the dynamic access lookup is meant to be used for dynamic key-value structures, like maps and keywords, and not by static ones like structs.

有两种方法可以实现所需的目标：

There are two ways to achieve what you want:

1. 实施访问权限

使用 Access.key（：foo）代替：foo 。

我会使用（2）：

iex(1)> defmodule Bla do
...(1)>   defstruct [:b]
...(1)> end
iex(2)> s = [a: %Bla{b: "c"}]
[a: %Bla{b: "c"}]
iex(3)> get_in(s, [:a, Access.key(:b)])
"c"

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