Object initialization syntax

Question

I'm just starting out with F# and I can't find the syntax to do object initialization like in C# 3.

I.e. given this:

public class Person {
  public DateTime BirthDate { get; set; }
  public string Name { get; set; }
}

how do I write the following in F#:

var p = new Person { Name = "John", BirthDate = DateTime.Now };

Answer 1

You can do it like this:

let p = new Person (Name = "John", BirthDate = DateTime.Now)

Answer 2

the answer from CMS is definitely correct. Here is just one addition that may be also helpful. In F#, you often want to write the type just using immutable properties. When using the "object initializer" syntax, the properties have to be mutable. An alternative in F# is to use named arguments, which gives you a similar syntax, but keeps things immutable:

type Person(name:string, ?birthDate) =
  member x.Name = name
  member x.BirthDate = defaultArg birthDate System.DateTime.MinValue

Now we can write:

let p1 = new Person(name="John", birthDate=DateTime.Now)
let p2 = new Person(name="John")

The code requires you to specify the name, but birthday is an optional argument with some default value.