A let and do binding creates the primary constructor of a class and runs when an instance of a class is created.

A function is compiled into a member if it has a let binding. If the let binding is a value which is not used in any function or member, then it is compiled into a local variable of a constructor; otherwise, it is compiled into a field of the class.

The do expression executes the initialized code. As any extra constructors always call the primary constructor, let and do bindings always execute, irrespective of which constructor is called.

Fields that are created by let bindings can be accessed through the methods and properties of the class, though they cannot be accessed from static methods, even if the static methods take an instance variable as a parameter:

type Student(name) as self =
    let data = name
    do
        self.PrintMessage()
        member this.PrintMessage() = printf " Student name is %s" data