问题描述
在寻找有关内联函数的静态解析类型参数的信息时，我偶然发现了 FSharp.Core中的各种基本运算符:
Looking for information about statically resolved type parameters for inline functions I stumbled upon the definitions of various primitive operators in FSharp.Core:
let inline (+) (x: ^T) (y: ^U) : ^V =
CheckedAdditionDynamic<(^T),(^U),(^V)> x y
when ^T : int32 and ^U : int32 = (# "add.ovf" x y : int32 #)
when ^T : float and ^U : float = (# "add" x y : float #)
// <snip>
when ^T : ^T = ((^T or ^U): (static member (+) : ^T * ^U -> ^V) (x,y))
在when关键字上方的代码段中可以看出，该格式以以下格式使用:when expr1 = expr2用于各种内置类型.我猜想这是某种等效于如果T = int使用opcode add.ovf，否则如果...，否则执行该操作"的编译器.
As can be seen in the snippet above the when keyword is used in the format of: when expr1 = expr2 for various built-in types. I'm guessing that this is some sort of compiler equivalent of "if T=int use opcode add.ovf, else if ..., else do that".
但是，我在F#文档中找不到对这种语法的单个引用/解释.能够对F#有一定了解的人可以解释上面那段代码中发生的事情吗?
However, I could not find a single reference/explanation to this kind of syntax in the F# documentation. Could someone with some inside knowledge of F# explain what is going on in that snippet above?
推荐答案
用户卡斯滕(Carsten)对这个答案提供了以下评论，因为他认为这是错误的.
User Carsten has provided the following comment to this answer as he considers it to be wrong.
Carsten用户为此答案添加了一条附加评论:
User Carsten added an additional comment to this answer:
Carsten的第一条评论中提到的答案是用户John Palmer在2013年4月提出的，该链接指向他在(# ..... #)语法
The answer referred to in Carsten's first comment is by user John Palmer in April 2013 which links to this answer he provided on the (# ..... #) syntax, What is the (# ... #) syntax seen in F3 standard library implementation?
用户MisterMetaphor提供了一个答案，引用了在论坛上发表的帖子，内容如下:
User MisterMetaphor provided an answer quoting a posting in a forum that said the following:
并非如此.此功能的99.9％目的是用于操作 在FSharp.Core.dll中定义(在1.9.2.9及更低版本中称为fslib.dll).
Not really. The 99.9% purpose of this feature is for operations defined in FSharp.Core.dll (called fslib.dll in 1.9.2.9 and before).
有关when关键字的其他用途，请参见以下内容.
For other uses of the when keyword see the following.
此Microsoft文档介绍了使用when关键字来获取匹配的其他条件，匹配表达式(F#).
This Microsoft document describes using the when keyword for additional conditions on matching, Match Expressions (F#).
此Microsoft文档介绍了使用when关键字表示通用类型参数的约束，约束(F#).
This Microsoft document describes using the when keyword to express constraints for generic type parameters, Constraints (F#).
另请参阅此Microsoft文档，该文档描述了在各种设置中与when关键字匹配的模式，模式匹配(F#).
Also see this Microsoft document describing pattern matching with the when keyword in various settings, Pattern Matching (F#).
模式匹配"文档以及以下示例说明了以下内容.
The Pattern Matching document says the following along with several examples.
匹配表达式"文档连同示例说明了以下内容.
The Match Expression document says the following along with an example.
这篇关于FSharp.Core中未记录的"when"关键字用法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！