F#动态查找运算符(?)重载

Question

无法定义(?)类型上的运算符重载：

type Foo =
     val s : string
     new(s) = { s = s }
     static member (?) (foo : Foo, name : string) = foo.s + name

let foo = Foo("hello, ")
let hw  = foo? world

// error FS0043: The member or object constructor 'op_Dynamic'
// takes 2 argument(s) but is here given 1. The required signature
// is 'static member Foo.( ? ) : foo:Foo * name:string -> string'.

如果我为运算符定义使用独立的let-binding，则一切正常：

let (?) (foo : Foo) (name : string) = foo.s + name

let hw  = foo? world

但是我需要为类型Foo直接指定op_Dynamic运算符。第一个代码片段有什么问题？

使用F# 1.9.7.4 @ Visual Studio2010 Beta2

Answer 1

也许有一种更简单的方法(我会看看)，但这在紧要关头可以做到：

type Foo =     
    val s : string     
    new(s) = { s = s }     
    static member (?)(foo : Foo, name : string) = 
        foo.s + name

let inline (?) (o:^T) (prop:string) : ^U =
    (^T : (static member (?) : ^T * string -> ^U)(o,prop))

let foo = Foo("hello, ")
let hw  = foo ? world 
printfn "%s" hw