带有静态成员约束的泛型类型的类型推断失败 [英] Type inference failing on generic type with static member constraint
问题描述
我定义了以下类型(从代码简化):
I have defined the following type (simplified from code):
type Polynomial<'a when 'a :(static member public Zero : 'a)
and 'a: (static member (+): 'a*'a -> 'a)
and 'a : (static member (*): 'a*'a -> 'a) > =
| Polynomial of 'a list
with
static member inline (+) (x: Polynomial<'a> , y : Polynomial<'a>) : Polynomial<'a>=
match x,y with
|Polynomial xlist, Polynomial ylist ->
let longer, shorter =
if xlist.Length> ylist.Length then xlist, ylist
else ylist, xlist
let shorterExtended = List.append shorter (List.init (longer.Length - shorter.Length) (fun _ -> LanguagePrimitives.GenericZero<'a>))
List.map2 (+) longer shorterExtended |> Polynomial
当我建立时,我得到警告:
When I build I get the warning :
warning FS0193:当(^ a或^?23604):(static> member(+):^ a * ^?23604 - > ^?23605时,类型参数缺少约束' )'b / b>
warning FS0193: A type parameter is missing a constraint 'when ( ^a or ^?23604) : (static >member ( + ) : ^a * ^?23604 -> ^?23605)'
对最后一行中的更长一词。据我所知,它应该能够推断出它总是添加两个'a'成员。
我该如何摆脱这个问题?
on the word "longer" in the last line. As far as I can see it should be able to infer that it is always adding two members of 'a. How can I get rid of this?
推荐答案
这是一个有趣的问题,使用让
绑定函数而不是静态成员似乎不会触发相同的警告。假设在绑定和成员函数中静态类型参数的分辨率存在差异。
This is an interesting question, using a let
bound function instead of a static member doesn't seem to trigger the same warning. Presumably there are differences between the resolution of static type parameters in let bound and member functions.
module PolyAdder =
let inline addPoly x y =
match x,y with
|Polynomial xlist, Polynomial ylist ->
let (longer : ^a list), (shorter : ^a list) =
if xlist.Length > ylist.Length then xlist, ylist
else ylist, xlist
let shorterExtended : ^a list = shorter @ (List.init (longer.Length - shorter.Length) (fun _ -> LanguagePrimitives.GenericZero< ^a >))
// no warning here!
List.map2 (+) longer shorterExtended |> Polynomial
然后,您可以使用a扩展 Polynomial
+运算符基于上面的限制函数:
You can then extend Polynomial
with a + operator based on the let bound function above:
type Polynomial with
static member inline (+) (x, y) = PolyAdder.addPoly x y
仍然没有警告,+运算符正常工作
There is still no warning and the + operator works normally
let poly1 = [1; 2; 5; 6; 8] |> Polynomial
let poly2 = [7; 1; 2; 5;] |> Polynomial
let polyAdded = poly1 + poly2
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