F＃静态成员类型约束 [英] F# Static Member Type Constraints

问题描述

我试图定义一个函数，factorize，它使用结构类型约束（需要静态成员零，一，+和/）类似于Seq.sum，以便它可以与int，long，bigint，等等。我似乎不能得到正确的语法，并且找不到很多关于这个主题的资源。

 让inline factorize（n：^ NUM）= 
 ^ NUM： （static member get_Zero：unit->（^ NUM））
 ^ NUM：（static member get_One：unit->（^ NUM））
 let rec factorize（n：^ NUM） ：^ NUM）（flist：^ NUM list）= 
如果n = ^ NUM.One then flist 
 elif n％j = ^ NUM.Zero then factorize（n / j）（^ NUM.One + ^ NUM.One）（j :: flist）
 else factorize n（j + ^ NUM.One）（flist）
 factorize n（^ NUM.One + ^ NUM.One）[] 
  

解决方案

这里是我写的：

 模块NumericLiteralG = begin 
 let inline FromZero（）= LanguagePrimitives.GenericZero 
 let inline FromOne（）= LanguagePrimitives.GenericOne 
 end 
 
 let inline factorize n = 
 let rec factorize nj flist = 
 if n = 1G then flist 
 elif n％j = 0G then factor （n / j）j（j :: flist）
 else factorize n（j + 1G）（flist）
 factorize n（1G + 1G）[] 
  

这里推断的factorize类型太笼统了，但是函数会按照你的期望工作。如果您希望通过向某些通用表达式添加显式类型，可以强制使用更加完整的签名和约束集：

  let inline factorize（n：^ a）：^ a list = 
 let（one：^ a）= 1G 
 let（zero：^ a）= 0G 
 let rec factorize n ^ a）flist = 
 if n = one then flist 
 elif n％j = zero then factorize（n / j）j（j :: flist）
 else factorn ）（flist）
因式分解n（一+一）[] 
  

I'm trying to define a function, factorize, which uses structural type constraints (requires static members Zero, One, +, and /) similar to Seq.sum so that it can be used with int, long, bigint, etc. I can't seem to get the syntax right, and can't find a lot of resources on the subject. This is what I have, please help.

let inline factorize (n:^NUM) =
    ^NUM : (static member get_Zero: unit->(^NUM))
    ^NUM : (static member get_One: unit->(^NUM))
    let rec factorize (n:^NUM) (j:^NUM) (flist: ^NUM list) = 
        if n = ^NUM.One then flist
        elif n % j = ^NUM.Zero then factorize (n/j) (^NUM.One + ^NUM.One) (j::flist)
        else factorize n (j + ^NUM.One) (flist)
    factorize n (^NUM.One + ^NUM.One) []

解决方案

Here's how I'd write it:

module NumericLiteralG = begin
  let inline FromZero() = LanguagePrimitives.GenericZero
  let inline FromOne() = LanguagePrimitives.GenericOne
end

let inline factorize n = 
  let rec factorize n j flist =  
    if n = 1G then flist 
    elif n % j = 0G then factorize (n/j) j (j::flist) 
    else factorize n (j + 1G) (flist) 
  factorize n (1G + 1G) [] 

The type inferred for factorize here is way too general, but the function will work as you'd expect. You can force a more sane signature and set of constraints if you want by adding explicit types to some of the generic expressions:

let inline factorize (n:^a) : ^a list = 
  let (one : ^a) = 1G
  let (zero : ^a) = 0G
  let rec factorize n (j:^a) flist =  
    if n = one then flist 
    elif n % j = zero then factorize (n/j) j (j::flist) 
    else factorize n (j + one) (flist) 
  factorize n (one + one) []

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