Implementing pattern matching in C#

Question

In Scala, you can use pattern matching to produce a result depending on the type of the input. For instance:

val title = content match {
    case blogPost: BlogP         


        

Answer 1

Generic implementation I'm using, that can match against the type, condition or a value:

public static class Match
{
    public static PatternMatch With(T value)
    {
        return new PatternMatch(value);
    }

    public struct PatternMatch
    {
        private readonly T _value;
        private R _result;

        private bool _matched;

        public PatternMatch(T value)
        {
            _value = value;
            _matched = false;
            _result = default(R);
        }

        public PatternMatch When(Func condition, Func action)
        {
            if (!_matched && condition(_value))
            {
                _result = action();
                _matched = true;
            }

            return this;
        }

        public PatternMatch When(Func action)
        {
            if (!_matched && _value is C)
            {
                _result = action((C)(object)_value);
                _matched = true;
            }
            return this;
        }


        public PatternMatch When(C value, Func action)
        {
            if (!_matched && value.Equals(_value))
            {
                _result = action();
                _matched = true;
            }
            return this;
        }


        public R Result => _result;

        public R Default(Func action)
        {
            return !_matched ? action() : _result;
        }
    }
}

And in your case, usage would look like:

Match.With(content)
     .When(blogPost => blogPost.Blog.Title)
     .When(blog => blog.Title)
     .Result; // or just .Default(()=> "none");

Some other examples:

var result = Match.With(new Foo() { A = 5 })
    .When(foo => foo.A)
    .When(bar => bar.B)
    .When(Convert.ToInt32)
    .Result;
Assert.Equal(5, result);

var result = Match.With(n)
    .When(x => x > 100, () => "n>100")
    .When(x => x > 10, () => "n>10")
    .Default(() => "");
Assert.Equal("n>10", result);

 var result = Match.With(5)
     .When(1, () => "1")
     .When(5, () => "5")
     .Default(() => "e");
 Assert.Equal("5", result);