Add fluent extension method for options classes so that we can create instances conveniently.

[edwardmeng]

No description provided.

[ejsmith]

This looks pretty good @edwardmeng. Only thing I was thinking different was to use a separate OptionsBuilder where all the extension methods live off of that so that they don't pollute the actual options object itself:

public class OptionsBuilder<T> where T: class, new() {
    public T Target { get; } = new T();
}

public class MyImp {
    private readonly MyImpOptions _options;

    public MyImp(ConfigureOptions<MyImpOptions> builder)
        : this(builder(new OptionsBuilder<MyImpOptions>()).Target) {}

    public MyImp(MyImpOptions options) {
        _options = options;
    }
}

public delegate OptionsBuilder<T> ConfigureOptions<T>(OptionsBuilder<T> builder) where T: class, new();

public class MyImpOptions {
    public string SomeOption { get; set; }
}

public static class MyImpOptionsBuilder {
    public static OptionsBuilder<MyImpOptions> WithSomeOption(this OptionsBuilder<MyImpOptions> builder, string someOption) {
        builder.Target.SomeOption = someOption;
        return builder;
    }
}

public static class Startup {
    public static void Main() {
        var myImp = new MyImp(b => b.WithSomeOption("value"));

        var myImp2 = new MyImp(new MyImpOptions { SomeOption = "value" });
    }
}

[ejsmith]

I’ve always been torn on fluent builder methods being prefixed with something like o => o.WithSomeOption() vs just having o => o.SomeOption(). What do you guys think @edwardmeng @niemyjski ?

[edwardmeng]

@ejsmith I have completed the changes as your suggestion, please review again.

[ejsmith]

Looks good except I like creating a delegate so that the ctors get a little simler and go from:

public InMemoryFileStorage(Action<IOptionsBuilder<InMemoryFileStorageOptions>> config)
    : this(OptionsBuilder<InMemoryFileStorageOptions>.Build(config)) { }

to

public delegate OptionsBuilder<T> ConfigureOptions<T>() where T: class, new();

public InMemoryFileStorage(ConfigureOptions<InMemoryFileStorageOptions> config)
    : this(OptionsBuilder<InMemoryFileStorageOptions>.Build(config)) { }

[edwardmeng]

I have tried as your suggestion, but the ConfigureOptions cannot be defined covariant between base options and inherited options.

[ejsmith]

Ok then I think it’s good to go.