f# function that returns a generic function

Question

I would like to do the following :

module private repo =
    let SaveEvts<'T> (conn:IConnection) mydata =  
        async {
            let! result = conn.SaveAsync(mydata)
        }

let SaveAsync (conn:IConnection) = repo.SaveEvts conn

so that I could open a single connection to my db and then have in closure my connection whenever I want to save some type T data. eg :

type Foo = { idPhoto : Guid }
type Bar = { reason : string }

let myConnection = new Connection(connectionString)
let save = SaveAsync myConnection
let doProgram =
    save<Foo>({idPhoto = 212313})
    save<Bar>({idPhoto = 212313})

This is fantasy writing, I do not know if it compiles: My issues here are

1. Is there a way to do what I want to achieve , ie a normal function that returns a generic function.
2. if it is doable, is it advisable?

I would like to avoid writing :

let saveFoo = SaveEvts<Foo> (conn:IConnection) 
let saveBar = SaveEvts<Bar> (conn:IConnection) 

but maybe there is no other way...

Answer 1

You cannot write a function that returns a generic function in F#. There are two ways to solve this:

• You can write a function that returns a simple object with a generic method and then use this object to do all the work
• You can define a new generic function that captures an existing connection

So, the code in your second snippet would not work, but you can do:

let myConnection = new Connection(connectionString)
let save arg = SaveAsync myConnection arg

save {FooProperty = 212313}
save {BarProperty = 212313}

Here, save is defined as a function and so it can be generic, but it can still capture the existing opened connection myConnection and use it for all the different arguments that you give it.