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is the new keyword optional? & object expressions
f#

Hello,

Am I right to assume that
let x = new System.Text.StringBuilder()
and
let x = System.Text.StringBuilder()
are identical? I am confused as to when I have to put it in the 'new' keyword and when I don't have to.

Also,
type Foo(x : int) =
member v.MyX() = x;;
let foo = {new Foo(3) with member v.MyX() = 4};;

I would expect foo.MyX() to return 4, but it returns 3. How come the MyX() member that I defined in the object expression doesn't overwrite the original MyX() of Foo?

Thanks.
~n

.

type Foo(x : int) =
member v.MyX() = x;;
let foo = {new Foo(3) with member v.MyX() = 4};;

Add an abstract definition for MyX, then make the original definition the default:

#light
type Foo(x : int) =
abstract member MyX : int
override it.MyX :int = x

{new Foo(3) with member it.MyX = 4}.MyX
--returns "4" as you desired.

NOTE: I removed the "()", because the abstract member definition needed a type declaration, and that was the only way I knew how to declare a type for a member that takes no arguments.

~TMSteve

By on 3/15/2008 9:44 PM ()

Here is a unit function decleration

abstract member MyX : unit -> int

By on 3/15/2008 9:54 PM ()

Hi namin,
Yes they are identical and yes new is optional. but I think it is a good practice to use it.

For the second part, myX is not an abstract function to override. Actually I would also suspect to hide the member and print as 4, but at the end the expression returns a type of Foo, there is no inheritence or override going in the expression. So the method that you have hidden is not called

Regards

By on 3/12/2008 5:09 PM ()

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