我如何根據f＃中的類型定義的對象生成新的不可變對象？

Question

我有這個代碼不工作

type Option(xsdLocation:string, xmlDirectory:string) = 
    member this.XsdLocation = xsdLocation 
    member this.XmlDirectory = xmlDirectory 

let a1 = new Option("xsd","xml") 
let a2 = {a1 with XsdLocation = "xsd2"} 

我得到的錯誤 error FS1129: The type 'Option' does not contain a field 'XsdLocation'

Answer 1

所定義的對象是一個標準的.NET class，不是record。如果你想使用with語法，你應該把它定義爲這樣的：

type Option = {XsdLocation : string; XmlDirectory : string} 

let a1 = {XsdLocation = "xsd"; XmlDirectory = "xml"} 
let a2 = {a1 with XsdLocation = "xsd2"} 

PS：我也建議選擇比Option以外的名稱爲您的類型，因爲Option是內置型。