我知道这在C#中是可能的,它产生了简单高效的代码。---同一类的两个对象可以访问彼此的私有部分。
class c1
{
private int A;
public void test(c1 c)
{
c.A = 5;
}
}
但这在F#中似乎是不可能的,是真的吗?
type c1()
let A = 0
member test (c: c1) = c.A
有趣的问题。它似乎适用于显式字段,但不适用于let绑定:
// Works
type c1 =
val private A : int
new(a) = { A = a }
member m.test(c : c1) = c.A
let someC1 = new c1(1)
let someMoreC1 = new c1(42);
let theAnswer = someC1.test someMoreC1
// Doesn't work
type c2() =
let mutable A = 42
// Compiler error: The field, constructor or member 'A' is not defined
member m.test(c : c2) = c.A
是的,但在您的示例中,A
在语义上不是c1
的私有成员,它更像是构造函数的局部变量。
@afrishke给出了一个如何用实际的私有成员A
(使用val
字段)定义c1
的例子。
正如F#规范第8.6.1.3节所述:
实例定义定义的函数和值在词法上对所定义的对象起作用(因此隐式地私有)。
这是可能的,并且被广泛使用,例如,用于检查成员相等性:
type c1 =
member private this.A = 0
interface IEquatable<c1> with
member this.Equals (that: c1) = this.A = that.A
// of course, it can be done in a regular method as well
member this.Equals (that: c1) = this.A = that.A
您只需在实例方法中直接使用a
type c1()
let A = 0
member x.test = A
对于静态方法,这是不起作用的,因为let绑定略有不同——那么您需要像这样的类定义
type c1()
private member x.A = 0
static member test (A:c1) = A.A