F# force an overload of System.String.Format

Question

I would like to format a string using `System.String.Format` which has 5 overloads: ``` String String.Format(String format , Object arg0 ) String String.Format(String format , Object arg0 , Object arg1 ) String String.Format(String format , Object arg0 , Object arg1 , Object arg2 ) String String.Format(String format , params Object[] args ) String String.Format(IFormatProvider provider , String format , params Object[] args ) ``` I would like to use the fourth overload (the one that takes an array of objects) like this: ``` let frm = "{0} - {1}" let args = [| 1; 2 |] System.String.Format(frm, args) ``` The problem is that the args argument is interpreted as an Object and hence the first overload is called. So correctly I get the following error: ``` System.FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list. ``` Is there a way to force the "correct" overload?

Accepted Answer

A more elegant variant of @John's answer is to add type annotation so that the compiler will do automatic upcast on all elements of an array:

```
let frm = "{0} - {1}"
let args : obj [] = [| 1; 2 |]
System.String.Format(frm, args)
```

F# force an overload of System.String.Format

Solution

Problem