F#中的空聚合运算符？

在编译时,对于使用(‘a Nullable,a) – > a或(‘a when’a：null,’a) – >的正确的重载’一个单一的运算符可以内联.甚至(‘a选项’a) – > ‘可以投入更多的灵活性.

为了提供更接近c#操作符的行为,我使默认参数’一个懒惰,所以它的源不被调用,除非原始值为空.

例：

let value = Something.PossiblyNullReturned()
            |?? lazy new SameType()

执行：

NullCoalesce.fs [Gist]：

//https://gist.github.com/jbtule/8477768#file-nullcoalesce-fs
type NullCoalesce =  
    static member Coalesce(a: 'a option,b: 'a Lazy) = match a with Some a -> a | _ -> b.Value
    static member Coalesce(a: 'a Nullable,b: 'a Lazy) = if a.HasValue then a.Value else b.Value
    static member Coalesce(a: 'a when 'a:null,b: 'a Lazy) = match a with null -> b.Value | _ -> a

let inline nullCoalesceHelper< ^t,^a,^b,^c when (^t or ^a) : (static member Coalesce : ^a * ^b -> ^c)> a b = 
                                            ((^t or ^a) : (static member Coalesce : ^a * ^b -> ^c) (a,b))

let inline (|??) a b = nullCoalesceHelper<NullCoalesce,_,_> a b