CODEWITHSUNDEEP
f#
user3116322
user3116322

Reputation:

F# Tuples with a base type

Is it possible to use tuples and class hierarchies together?

I cannot get a function to accept a tuple parameter which is an abstract type:

[<AbstractClass>]
type XBase () = 
    member val Name="" with get, set 

type X () = 
    inherit XBase ()  

type Y () = 
    inherit XBase ()  

//fine without tuples
let f(values:seq<XBase>) =       
    printf "ok."

f [new X(); new Y()]

//this function won't work 
let f1<'V when 'V :> XBase>(keysAndValues:seq<'V * string>) =       
    printf "ok."

//compiler error: This expression was expected to have type X but here it has type Y
//f1 [(new X(), ""); (new Y(), "")]

System.Console.ReadLine()

Upvotes: 1

Views: 136

Answers (1)

Petr
Petr

Reputation: 4280

Tuples in your commented sequence are not derived from the same base class. Tuple of type (XBase * string) is not a base class for tuple class (X * string) or (Y * string) So these concrete instances of 2 different types cannot be put in the collection together. I think it's true for any .NET language (C#, VB) also.

So you cannot create this sequence:

let tuples = [(new X(), ""); (new Y(), "")]

But you can invoke your f1 functions with these 2 sequences:

f1 [(new X(), ""); (new X(), "")]
f1 [(new Y(), ""); (new Y(), "")]

Upvotes: 4

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