# generics f# constraints - Functions with generic parameter types

This works:

```
type T = T with
static member ($) (T, n:int ) = int (sqrt (float n))
static member ($) (T, n:int64) = int64 (sqrt (float n))
let inline sqrt_int (x:'t) :'t = T $ x
```

It uses static constraints and overloading, which makes a compile-time lookup on the type of the argument.

The static constraints are automatically generated in presence of an operator (operator `$`

in this case) but it can always be written by hand:

```
type T = T with
static member Sqr (T, n:int ) = int (sqrt (float n))
static member Sqr (T, n:int64) = int64 (sqrt (float n))
let inline sqrt_int (x:'N) :'N = ((^T or ^N) : (static member Sqr: ^T * ^N -> _) T, x)
```

More about this here.

I am trying to figure out how to define a function that works on multiple types of parameters (e.g. int and int64). As I understand it, function overloading is not possible in F# (certainly the compiler complains). Take for example the following function.

```
let sqrt_int = function
| n:int -> int (sqrt (float n))
| n:int64 -> int64 (sqrt (float n))
```

The compiler of course complains that the syntax is invalid (type constraints in pattern matching are not supported it seems), though I think this illustrates what I would like to achieve: a function that operates on several parameter types and returns a value of the according type. I have a feeling that this is possible in F# using some combination of generic types/type inference/pattern matching, but the syntax has eluded me. I've also tried using the :? operator (dynamic type tests) and *when* clauses in the pattern matching block, but this still produces all sorts errors.

As I am rather new to the language, I may very well be trying to do something impossible here, so please let me know if there is alternative solution.

Here's another way using runtime type checks...

```
let sqrt_int<'a> (x:'a) : 'a = // '
match box x with
| :? int as i -> downcast (i |> float |> sqrt |> int |> box)
| :? int64 as i -> downcast (i |> float |> sqrt |> int64 |> box)
| _ -> failwith "boo"
let a = sqrt_int 9
let b = sqrt_int 100L
let c = sqrt_int "foo" // boom
```