C# Error message: Cannot Implicitly convert type

Question

The code below throws the following exception:

Error 1 Cannot implicitly convert type 'Clarity.DevTest.Exercises.ChessPosition' to 'System.Collections.Generic.IEnumerable< Clarity.DevTest.Exercises.ChessPosition>'. An explicit conversion exists (are you missing a cast?)

Can someone explain to me whats going wrong and why it cant return the result?

using System;
using System.Collections.Generic;

namespace Clarity.DevTest.Exercises
{
public class Exercise1
{
    public IEnumerable<ChessPosition> GetLegalMoves(ChessPosition rookToMove, ChessPosition friendlyRook, ChessPosition enemyRook1, ChessPosition enemyRook2)
    {

        //create array to hold positions
        ChessPosition[,] coords = new ChessPosition [8,8];
        //set the Rooks into the correct places on the array
        //eg rookToMove.X = 4, rookToMove.Y = 5, "R" would be places in 4,5
        coords[rookToMove.X, rookToMove.Y] = "R";
        coords[friendlyRook.X, friendlyRook.Y] = "F";
        coords[enemyRook1.X, enemyRook1.Y] = "1";
        coords[enemyRook2.X, enemyRook2.Y] = "2";

        //throw new NotImplementedException();

        ChessPosition result = new ChessPosition(4, 5);
        return result;
    }
}

public partial class ChessPosition
{
    public ChessPosition(int x, int y)
    {
        //check to see if out of bounds
        if (x < 1 || x > 8 || y < 1 || y > 8)
        {
            throw new ArgumentException("x and y must be in the range 1-8");
        }
        X = x;
        Y = y;
    }

    public int X { get; set; }
    public int Y { get; set; }
  }
}

David L · Accepted Answer · 2015-05-22 20:41:28Z

2

You're returning a single ChessPosition instead of an Enumerable collection of results.

Either return an enumerable collection:

ChessPosition result = new ChessPosition(4, 5);
IEnumerable<ChessPosition> results = new List<ChessPosition>();
results.Add(result);

return results;

or change your return type:

public ChessPosition GetLegalMoves(
    ChessPosition rookToMove, ChessPosition friendlyRook, ChessPosition 
    enemyRook1, ChessPosition enemyRook2)

answered May 22, 2015 at 20:41

David L

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Jonesopolis · Accepted Answer · 2015-05-22 20:40:52Z

2

your method says it's returning a IEnumerable<ChessPosition> but you actually return a ChessPosition.

your method signature is:

public IEnumerable<ChessPosition> GetLegalMoves(...

So you are telling anyone who accesses that method they will receive a collection of ChessPosition.

But you return:

ChessPosition result = new ChessPosition(4, 5);
return result;

which is not a collection, but a single ChessPosition.

You need to decide whether your method returns either a single ChessPosition, or many.

answered May 22, 2015 at 20:40

Jonesopolis

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Comments

Adam Diament · Accepted Answer · 2015-05-22 20:41:14Z

1

The return type of your method 'GetLegalMoves' does not match what you are returning - change the return type to remove the ienumerable, so it's just returning 'ChessPosition'

answered May 22, 2015 at 20:41

Adam Diament

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