CODEWITHSUNDEEP
f#discriminated-union
John Doe
John Doe

Reputation: 493

Discriminated union with an already defined class

I have the School class (with 2 constructors):

type School(name, antiquity) = 
    member this.Name: string = name
    member this.Antiquity: int = antiquity

    new(name) = School(name, 0)

And the types of building:

type Building =
| House
| School of School

And I want know what type is a building with the function "knowType":

let knowType building =
    match building with
    | House -> "A house!"
    | School -> "A school" // Error

The error in "knowType" is in the second case: "The constructor is applied to 0 arguments, but expect 1".

Upvotes: 1

Views: 79

Answers (1)

John Palmer
John Palmer

Reputation: 25516

It should be 

let knowType building =
    match building with
    | House -> "A house!"
    | School _ -> "A school"

You need to give a variable for the of School part. _ just means it is ignored

Upvotes: 6

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