Back to Questions
1.8k
views2
comments
How to convert System.Object into a List or Array?
f#

Hello-

I have an external API that returns an array of values (into the variable "data") below. The return type is System.Object, by definition. In VS 2010 I can see that this code works, because I can hover over data and see that it is an object[] that contains the numeric data I was expecting. However, I can't do any sort of iteration with it because I can't figure out how to construct an F# type like List or Array, and System.Object doesn't have that capability. None of the constructors appear willing to accept an "obj" as an argument. Any ideas?

let factset = FactSet_API_LIB.FactSet_APIClass();
let dateTimeSpan: obj[] = Array.zeroCreate 3;
dateTimeSpan.[0] <- box startDate;
dateTimeSpan.[1] <- box endDate;
dateTimeSpan.[2] <- box freq;
let data = factset.FetchData(cusip, fql, ref dateTimeSpan);

.

If you have an object whose run-time type is more specific than its compile-time type, then you can recover the type information with a downcast or a type test.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

 

let oa : obj[] = [| box 42; box "hello" |]
let o : obj = box oa

// now recover types
// I know o is actually an object array at runtime
let newoa = o :?> obj[]
// I know the first element is an int
let i = newoa.[0] :?> int
printfn "%d" i
// if I'm not sure, I can type test
match newoa.[1] with
| :? int as i -> printfn "the int %d" i
| :? string as s -> printfn "the string %s" s
| _ -> printfn "something else"
By on 1/27/2010 11:29 AM ()

Aha - This works! Thanks so much.

By on 1/27/2010 1:27 PM ()

    Topic tags

    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper