How to convert beta4 code to beta5 when parseResult.GetValue() may return a null?

[ptr727]

I am converting a project from Beta4 to Beta5.

I can mostly convert without issue, but now that Option<T> does not support cast to T I need to use parseResult.GetValue(option), and that may return a null making lots of work to get rid of warnings.

Is there not an easier way?

        // Converted to B5 format
        Option<string> versionOption = new("--version")
        {
            Description = "Version JSON file.",
            DefaultValueFactory = _ => "./Make/Version.json",
        };

        // Converted to B5 format
        Command matrixCommand = new("matrix", "Create matrix information file")
        {
            versionOption,
            matrixOption,
            updateOption,
        };
        matrixCommand.SetAction(parseResult =>
        {
            return MatrixHandler(
                parseResult.GetValue(versionOption), // Possible null reference
                parseResult.GetValue(matrixOption),
                parseResult.GetValue(updateOption)
            );
        });

        // B4 format
        Command schemaCommand = new("schema", "Write Version and Matrix JSON schema files")
        {
            schemaVersionOption,
            schemaMatrixOption,
        };
        schemaCommand.SetAction(SchemaHandler, schemaVersionOption, schemaMatrixOption);

Is there a way to pass the options that will guarantee a T type that is either the parsed value of the default value, but not null?

[jonsequitur]

Are you seeing null being returned for your versionOption or are you referring to the fact that it returns T? The use of DefaultValueFactory means that (unless there's a bug) it shouldn't actually return null. To avoid the cast, you can call ParseResult.GetRequiredValue instead. This returns T instead of T?. Also note that if the value can't be returned (e.g. you use it for an option that's not marked as Required or doesn't have a default value set), it will throw.

Some details of how this works are being hashed out in #2601.

[ptr727]

I meant that everywhere I use GetValue() I get linter warnings about e.g. Possible null reference argument for parameter 'versionPath' in 'Task<int> Program.VersionHandler(string versionPath)'.

Using GetRequiredValue() makes the linter happy.

To confirm, if I use GetRequiredValue(), and the value is not set on the commandline, but I did set a DefaultValueFactory, then the default will be returned?

[jonsequitur]

To confirm, if I use GetRequiredValue(), and the value is not set on the commandline, but I did set a DefaultValueFactory, then the default will be returned?

That's the goal. One of the changes in #2601 is to keep that guarantee even if, for example, --help was requested.

[arielcostas]

GetValue returns T? by default, meaning for an Option<string> it will return string? (nullable). GetRequiredValue seems to return the type itself and use the DefaultValueFactory if it's not provided.

RootCommand command = new RootCommand("Example - Does something");
Option<string> nameOption = new Option<string>("--name")
{
    Description = "Your name",
    DefaultValueFactory = _ => "World"
};

command.Options.Add(nameOption);
command.SetAction(pr =>
{
    string name = pr.GetRequiredValue(nameOption);
    Console.WriteLine($"Hello, {name}!");
});

command.Parse(args).Invoke();

Calling the former program with --name ptr727 will print "Hello, ptr727!", and calling it without arguments will print "Hello, World!".

If the DefaultValueFactory is not set and no value is provided, a System.InvalidOperationException is thrown when calling GetRequiredValue.

So, to summarise:

• If the value is compulsory or has a fallback factory, use GetRequiredValue
• If the value is optional (nullable), or you'll coalesce it in the Action, use GetValue (returning T?). For example: string name = pr.GetValue(nameOption) ?? "World";. But then the --help won't show the default.