CODEWITHSUNDEEP
f#
Aldo Ortega
Aldo Ortega

Reputation: 25

A function that accepts multiple types

I am fairly new to f#, but I want to know if it is possible to make a function that accepts multiple types of variables.

let add x y = x + y
let integer = add 1 2
let word = add "He" "llo"

Once a function use a type of variable it cannot accept another one.

Upvotes: 1

Views: 218

Answers (1)

JL0PD
JL0PD

Reputation: 4488

You need to read about statically resolved type parameters and inline functions. It allows to create functions which may take any type that supports operation and/or have member. So your add function should be defined this way:

let inline add x y = x + y

Don't overuse inlined functions because their code inlined in call site and may increase assembly size, but may increase performance (test each case, don't make predictions!). Also inlined function are supported only by F# compiler and may not work with other languages (important when designing libraries).

Example of SRTP magic:

let inline (|Parsed|_|) (str: string) =
    let mutable value = Unchecked.defaultof<_>
    let parsed = ( ^a : (static member TryParse : string * byref< ^a> -> bool) (str, &value))
    if parsed then
        Some value
    else
        None

match "123.3" with
| Parsed 123 -> printfn "int 123"
| Parsed 123.4m -> printfn "decimal 123.4"
| Parsed 123.3 -> printfn "double 123.3"
// | Parsed "123.3" -> printfn "string 123.3" // compile error because string don't have TryParse static member
| s -> printfn "unmatched %s" s

Upvotes: 3

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