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如何在Nim中声明可为null的字段?

nim-lang

0

Alex Craft · 技术社区 · 4 年前

这个 stock_symbol 是可选的,它只存在于某些公司,在Nim中声明它的正确方式是什么?

我一定要用吗 ref 或者还有别的办法?

type
  Company = object
    name:         string
    stock_symbol: string

echo Company(name: "Microsoft", stock_symbol: "MSFT")
echo Company(name: "Kinetic",   stock_symbol: nil)

而对于复合型的类似问题,通常你需要同时知道证券交易所和符号

type
  SymbolWithExchange = object
    exchange: string
    symbol:   string

  Company2 = object
    name:         string
    stock_symbol: SymbolWithExchange

echo Company2(
  name:         "Microsoft", 
  stock_symbol: SymbolWithExchange("NYSE", "MSFT")
)
echo Company2(name: "Kinetic",   stock_symbol: nil)

0 回复 | 直到 4 年前

1

3

Alex Craft 4 年前

好像 Option[T] 应使用

import options

type
  Company = object
    name:         string
    stock_symbol: Option[string]

echo Company(name: "Microsoft", stock_symbol: some("MSFT"))
echo Company(name: "Kinetic",   stock_symbol: none(string))

和

import options

type
  SymbolWithExchange = object
    exchange: string
    symbol:   string

  Company2 = object
    name:         string
    stock_symbol: Option[SymbolWithExchange]

echo Company2(
  name:         "Microsoft", 
  stock_symbol: some(SymbolWithExchange(exchange: "NYSE", symbol: "MSFT"))
)
echo Company2(name: "Kinetic",   stock_symbol: none(SymbolWithExchange))

2

3

Gibus 4 年前

使用“options”模块是可能的,但我发现它带来的问题比它解决的问题要多,因为您需要将输入作为some()进行排序,如果您正在构建一个库或者其他人将使用这个库,那么这个要求可能是一个大问题。

在您的例子中,我建议使用构造函数初始化值。

type
  Company = object
    name:         string
    stock_symbol: string

proc company_constructor(name: string, stock_symbol: string = ""): Company =
  return Company(name:name, stock_symbol:stock_symbol)

let
  company_a = company_constructor("Microsoft", "MSFT")
  company_b = company_constructor("Kinetic")

echo company_a
echo company_b

输出:

(name: "Microsoft", stock_symbol: "MSFT")
(name: "Kinetic", stock_symbol: "")