F#记录成员评估 [英] F# record member evaluation

问题描述

为什么每次通话都会评估t.b?并且有什么方法可以使它只评估一次?

Why is t.b evaluated on every call? And is there any way how to make it evaluate only once?

type test =
  { a: float }
  member x.b =
    printfn "oh no"
    x.a * 2.

let t = { a = 1. }
t.b
t.b

推荐答案

这是一个属性；您基本上是在呼叫get_b()成员.

It's a property; you're basically calling the get_b() member.

如果您希望效果在构造函数中发生一次，则可以使用一个类:

If you want the effect to happen once with the constructor, you could use a class:

type Test(a:float) =
    // constructor
    let b =   // compute it once, store it in a field in the class
        printfn "oh no"
        a * 2.
    // properties
    member this.A = a
    member this.B = b

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