C#'s 'dynamic' in F#

Question

One example of using the DLR in C# is as follows:

dynamic dyn = new MyObject();
dyn.MyMethod(); //resolved at runtime

what would be the equivalent in F#?

Thanks.

Answer 1

The ? operator has similar expressive power to the dynamic keyword in C# (but it can be only used for reading of properties, method invocation and setting of properties).

There is no built-in implementation that would allow you to dynamically use properties or methods of a .NET class (via Reflection or DLR), but there are some fairly solid implementations from the community. This has been discussed in another SO question before.

There are also implementations of ? that allow you access some common data sources such as SQL databases. For example, this MSDN article includes a definition that allows you to write db?Query?Foo(1) to call a stored procedure named Foo.

For various other types (such as finding an element in XAML or accessing elements or attributes in XML document), the definition of ? is quite easy to write.

Answer 2

On the flip side, if you're trying to expose dynamic behavior to C# from F#, you can use DynamicAttribute^[MSDN]. For example, declaring a dynamic property might look like

type HasDynamicProperty() =
    [<Dynamic([|true|])>]
    member this.DynamicObject : obj = ...

which is used from C# like

var hdp = new HasDynamicProperty();
dynamic dynObj = hdp.DynamicObject;

Answer 3

There's a package called FSharp.Interop.Dynamic and that will make it possible to do a call to a dynamic object using the ? operator.

Answer 4

F# has the ? operator which you use like so:

 myVariable?SomePropertyThatIsNotDeclared

There is no dynamic keyword equivalent. Take a look at this article for how to use it https://weblogs.asp.net/podwysocki/using-and-abusing-the-f-dynamic-lookup-operator