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Richard Deeming wrote:

But it won't work, in the sense that the returned instance will be using the default connection string for the context, not the connection string from the instance passed in.

var context1 = new ModelDataContext(new SqlConnection("server=A;database=B"));
var context2 = new ModelDataContext(new SqlConnection("server=C;database=D"));

CreateNewContext(context1, out var newConn, out var newContext);

// As expected:
Console.WriteLine(newConn.ConnectionString == context1.Connection.ConnectionString); // True

// Not as expected:
Console.WriteLine(newContext.Connection.ConnectionString == context1.Connection.ConnectionString); // False
Console.WriteLine(newContext.Connection.ConnectionString == newConn.ConnectionString); // False
Console.WriteLine(newContext.Connection == newConn); // False

// Also not as expected:
Console.WriteLine(newContext.Connection.ConnectionString == context2.Connection.ConnectionString); // True

Richard Deeming wrote:

You could still break it though:

Main(...)
{
    new Program().Run();
}

public class Singleton
{
    private Singleton _current;

    public Singleton Current
    {
        get
        {
            if (_current == null)
            {
                _current = new Singleton();
            }

            return _current;
        }
    }

    private Singleton()
    {
    }
}

OriginalGriff wrote:

[~forename~}