why does performance improve when using `static let` over `static member`?-CodePudding

Not only did I see an improvement in performance after switching to IDictionary from Map (which is explored in a question from over 10 years ago), I got even more speed when I went from this type:

type MyCollection =

    static member Collection = [
        (1, "one")
        (2, "two")
        ...
    ] |> dict

    static member Get id = MyCollection.Collection[id]

…to a type like this:

type MyCollection() =

    static let collection = [
        (1, "one")
        (2, "two")
        ...
    ] |> dict

    static member Get id = collection[id]

Why does performance improve when using static let over static member?

CodePudding user response：

You can see the difference if you look at the decompilation in Sharplab

static member Collection compiles to a property with a getter. i.e. it is syntactic sugar for static member Collection() hence when you call MyCollection.Collection it creates a new IDictionary every call.

By contrast static let collection is essentially a standard binding to a value with special auto-initialisation code. It only creates the IDictionary once.