System.Version没有在F＃中实现System.IComparable

Question

I want to sort a sequence of Version objects in F#:

let maxVersion =
    versions
    |> Seq.max (fun version -> version)

The compiler produces the following error message:

The type '(seq -> 'a)' does not support the 'comparison' constraint. For example, it does not support the 'System.IComparable' interface

When I hit F12 in Visual studio to take a look at the metadata of Version it says that Version only implements ICloneable , but not IComparable . But when I go to sourceof.net it says it implements IComparable as well as some other interfaces.

Does F# use a different version of the .NET framework?

Answer 1

The error message is telling you that (seq->'a) does not implement IComparable which is true since (seq->'a) is a function, not a sequence.

If you look at the signature of Seq.max it takes only the sequence as parameter. Remove the lambda (fun version -> version) and it should be alright.

Otherwise, if you want to apply a key generator function for the sort, use instead Seq.maxBy