Add a possibility to retrieve the Maybe's value where a default value is returned for the none-Case

[marco-bertschi]

I'm thinking about the case where a Maybe<T> is used as a method parameter and a default value is known for the behavior in this method, for example:

public void Foo(Maybe<string> maybeBar = default)
{
   string defaultBar = "bar";
   maybeBar.Do(bar => defaultBar = bar);
}

This could be made a lot simpler with the following method wich should be added:

public void Foo(Maybe<string> maybeBar = default)
{
   // if 'bar' has a value, the value is returned, else 'defaultBar' is set to "bar"
   string defaultBar = maybeBar.ValueOrDefault("bar"); 
}

[marco-bertschi]

This would also allow us to have readonly properties set by a Maybe:

public class XmlTestOutputCompareAssertParameter
{
        public XmlTestOutputCompareAssertParameter(
            Maybe<string> aMaybeFileExtensionPattern = default)
        {
            aMaybeFileExtensionPattern.Do(aFileExtensionPattern => this.FileExtensionPattern = aFileExtensionPattern);
        }

        // Bad example: needs a private setter 
        public string FileExtensionPattern { get; private set; } = ".txt";
}

public class XmlTestOutputCompareAssertParameter
{
        public XmlTestOutputCompareAssertParameter(
            Maybe<string> aMaybeFileExtensionPattern = default)
        {
            this.FileExtensionPattern = aMaybeFileExtensionPattern.ValueOrDefault(".txt");
        }

        // Good example: Private setter isn't needed
        // Bonus: Default value and initialization via c'tor are together in one place.
        public string FileExtensionPattern { get; }
}

Overall, code would be cleaner as the Maybe-Pattern wouldn't enforce readonly properties to become properties with private setters when initializable via c'tor.

[marco-bertschi]

@stefan-lindegger Opinions?

[marco-bertschi]

offline discussion with @stefan-lindegger:

• We agree on the proposed feature
• Additionally, ThrowIfNone should be renamed to Value to ensure a consistent interface. Its behavior shouldn't change, though.

We also would like this to be a task for someone within BBT who hasn't had the chance to gather experience with GitHub yet to get their feet wet.