Porting C# to F#

Class Implementing an Interface

Classes implement an interface to meet the interface's contract. For example, a C# class may implement IDisposable,

public class Resource : IDisposable
{ 
    private MustBeDisposed internalResource;
    
    public Resource() 
    { 
        internalResource = new MustBeDisposed();
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing){
        if (disposing){
            if (resource != null) internalResource.Dispose();
        }
    }
}

To implement an interface in F#, use interface in the type definition,

type Resource() = 
    let internalResource = new MustBeDisposed()

    interface IDisposable with
        member this.Dispose(): unit = 
            this.Dispose(true)
            GC.SuppressFinalize(this)

    member __.Dispose disposing = 
        match disposing with 
        | true  -> if (not << isNull) internalResource then internalResource.Dispose()
        | false -> ()

POCOs

Some of the simplest kinds of classes are POCOs.

// C#
public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime Birthday { get; set; }
}

In F# 3.0, auto-properties similar to C# auto-properties were introduced,

// F#
type Person() = 
    member val FirstName = "" with get, set
    member val LastName = "" with get, set
    member val BirthDay = System.DateTime.Today with get, set

Creation of an instance of either is similar,

// C#
var person = new Person { FirstName = "Bob", LastName = "Smith", Birthday = DateTime.Today }; 
// F#
let person = new Person(FirstName = "Bob", LastName = "Smith")

If you can use immutable values, a record type is much more idiomatic F#.

type Person = { 
    FirstName:string; 
    LastName:string; 
    Birthday:System.DateTime 
} 

And this record can be created:

let person = { FirstName = "Bob"; LastName = "Smith"; Birthday = System.DateTime.Today }

Records can also be created based on other records by specifiying the existing record and adding with, then a list of fields to override:

let formal = { person with FirstName = "Robert" }