F# type functions and a [<GeneralizableValue>] attribute

问题

What is the difference between this two F# type functions:

let defaultInstance1<'a when 'a:(new: unit->'a)> = new 'a()

[<GeneralizableValue>]
let defaultInstance2<'a when 'a:(new: unit->'a)> = new 'a()

回答1:

let defaultInstance1<'a when 'a:(new: unit->'a)> = new 'a()

[<GeneralizableValue>]
let defaultInstance2<'a when 'a:(new: unit->'a)> = new 'a()

let x1 = defaultInstance1 // value restriction
let x2 = defaultInstance2

回答2:

Here is a good blog:

http://blogs.msdn.com/b/mulambda/archive/2010/05/01/value-restriction-in-f.aspx

It takes a bit of reading to get to the GeneralizableValue part, but if you get there, I think you will understand it. :)

来源：https://stackoverflow.com/questions/3963568/f-type-functions-and-a-generalizablevalue-attribute