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I know that in f# I can treat out parameters as members of a result tuple when I'm using them from F#, e.g.
(success, i) = System.Int32.TryParse(myStr)
What I'd like to know is how I define a member to have signature that appears to C# as having an out parameter.
Is it possible to do this? And can I just return a tuple and have the opposite process occur when I call the method from C#, e.g.
type Example() =
member x.TryParse(s: string, success: bool byref)
= (false, Unchecked.defaultof<Example>)
426
The out parameter in C# is used to pass arguments to methods by reference. It differs from the ref keyword in that it does not require parameter variables to be initialized before they are passed to a method. The out keyword must be explicitly declared in the method's definition as well as in the calling method.
Calling a method with an out argument TryParse method, which attempts to convert a string to a number. Starting with C# 7.0, you can declare the out variable in the argument list of the method call, rather than in a separate variable declaration.
Whenever we call a method with an parameter, we must have to declare that variable first, before we use it.
No. To make it "optional", in the sense that you don't need to assign a value in the method, you can use ref . A ref parameter is a very different use case.
No, you can't return the result as a tuple -- you need to assign the value to the byref value before returning the result from the function. Also note the [<Out>] attribute -- if you leave that out, the parameter acts like a C# ref parameter.
open System.Runtime.InteropServices
type Foo () =
static member TryParse (str : string, [<Out>] success : byref<bool>) : Foo =
// Manually assign the 'success' value before returning
success <- false
// Return some result value
// TODO
raise <| System.NotImplementedException "Foo.TryParse"
If you want your method to have a canonical C# Try signature (e.g., Int32.TryParse), you should return a bool from your method and pass the possibly-parsed Foo back through the byref<'T>, like so:
open System.Runtime.InteropServices
type Foo () =
static member TryParse (str : string, [<Out>] result : byref<Foo>) : bool =
// Try to parse the Foo from the string
// If successful, assign the parsed Foo to 'result'
// TODO
// Return a bool indicating whether parsing was successful.
// TODO
raise <| System.NotImplementedException "Foo.TryParse"
open System.Runtime.InteropServices
type Test() =
member this.TryParse(text : string, [<Out>] success : byref<bool>) : bool =
success <- false
false
let ok, res = Test().TryParse("123")
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