// Iteration 1

//-----------------------------------------------------------------------------------------

//

// Instructions:

//

// The following code is a slightly revised version of the last iteration, with some

// problematic code uncommented. It runs, but it doesn't compile cleanly.

//

// Can you fix it so that it compiles with no warnings and runs successfully?

​

using System;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {

        StringGatewayTests.IsNullOrWhiteSpace_NullValue_ReturnsTrue();

        StringGatewayTests.IsNullOrWhiteSpace_EmptyValue_ReturnsTrue();

        StringGatewayTests.IsNullOrWhiteSpace_AllWhiteSpaceValue_ReturnsTrue();

        StringGatewayTests.IsInterned_NullValue_ReturnsFalse();

        StringGatewayTests.IsInterned_StringLiteralValue_ReturnsTrue();

        StringGatewayTests.IsInternedV2_NullValue_ReturnsTrue();

    }

}

​

public static class StringGateway

{

    public static bool IsNullOrWhiteSpace(this string str) => string.IsNullOrWhiteSpace(str);

​

    public static bool IsInterned(this string str) => str is not null && string.IsInterned(str) is string;

​

    // The following line generates a compiler warning.

    // Why?

    // Can you fix it without changing the return type?

    public static string? IsInternedV2(this string str) => string.IsInterned(str);

}

​

public class StringGatewayTests

{

    public static void Assert(bool value)

    {

        Debug.Assert(value);

        "OK".Dump();

    }

​

    public static void IsNullOrWhiteSpace_NullValue_ReturnsTrue()

    {

        string Value = null;

        bool Result = Value.IsNullOrWhiteSpace();

        Assert(Result == true);

    }

​

    public static void IsNullOrWhiteSpace_EmptyValue_ReturnsTrue()

    {

        string Value = string.Empty;

        bool Result = Value.IsNullOrWhiteSpace();

        Assert(Result == true);

    }

​

    public static void IsNullOrWhiteSpace_AllWhiteSpaceValue_ReturnsTrue()

    {

        string Value = "    \r\n \t";

        bool Result = Value.IsNullOrWhiteSpace();

        Assert(Result == true);

    }

​

    public static void IsInterned_NullValue_ReturnsFalse()

    {

        string Value = null;

        bool Result = Value.IsInterned();

        Assert(Result == false);

    }

​

    public static void IsInterned_StringLiteralValue_ReturnsTrue()

    {

        string Value = "This is a test.";

        bool Result = Value.IsInterned();

        Assert(Result == true);

    }

​

    public static void IsInternedV2_NullValue_ReturnsTrue()

    {

        string Value = "a constant string";

        string Result = Value.IsInternedV2();

        System.Diagnostics.Debug.Assert(Result != null);

        "OK".Dump();

    }

}

​