can I define struct in a class in F#?

Question

this is example code in C# :

class exampleClass
{
    struct exampleStruct
    {
        public int number;
    }

    private exampleStruct[,] e;                    
    private enum exampleMove { Up, Down, Right, Left, Enter, Escape };
    Stack<int> returnPath;
    bool returntoBeg;
    int numRandomMoves;

    public exampleClass()
    {
        e = new exampleStruct[5, 5];
        exampleStruct ex;
        returntoBeg = false;
        returnPath = new Stack<int>();
        numRandomMoves = 0;

        for (int y = 0; y < 5; y++)
        {
            for (int x = 0; x < 5; x++)
            {
                ex = new exampleStruct();
                ex.number = 0

                e[x, y] = ex;
            }
        }
    }
}

I have an example code like above, i want to translate it into F#. But the problem is, when i make a class using F# and define struct in it, it shows errors and pointing that i can't declare type inside class type. Any help?

Why do you need such a feature? Just to port C# to F# line by line? — pad, Feb 01 '12 at 07:14
Probable duplicate: http://stackoverflow.com/questions/8948332/why-doesnt-f-support-nested-classes — kkm inactive - support strike, Feb 01 '12 at 11:31

Daniel · Accepted Answer · 2012-02-01T15:29:40.197

2

I think the following is a good workaround for nested types.

namespace MyNamespace

module private PrivateTypes =
  [<Struct>]
  type ExampleStruct(number: int) =
    member __.Number = number

open PrivateTypes

type ExampleClass() =
  let e = Array2D.init 5 5 (fun y x -> ExampleStruct(0))
  //other members

ExampleStruct is nested under PrivateTypes, which is only visible in the same file.

edited Feb 01 '12 at 15:29

answered Feb 01 '12 at 15:22

Daniel

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score 1 · Answer 2 · answered Feb 01 '12 at 11:40

While you cannot nest types, you can use intrinsic complex types that F# provides. Tuples are often a good data structure for data that has not very wide, observable scope, such as it is in your case.

In practice, I usually define implementation types in a module called e. g. Internal, and do not allow them to escape from the library. You may also define separate module per logical group of classes or even per complex class implementation.

can I define struct in a class in F#?

2 Answers2