Demo of a fluent api implementation for mapping one object to another. The unit test does not actually exercise the implementation, but it does demonstrate how the api will look to the consumer.

gistfile1.cs

    [Test]
    public void ApiDocumentation()
    {
        // Arrange
        var builder = Substitute.For<IBuilder>();
        builder.Create<string>().From(5.0m).Returns("Five");
        
        // Act
        var result = builder.Create<string>().From(5.0m);
        
        // Assert
        Assert.That(result, Is.EqualTo("Five"));
    }

    public interface IBuilder
    {
        IBuilderNode<TOutput> Create<TOutput>();
    }
      
    public interface IBuilderNode<out TOutput>
    {
        TOutput From<TInput>(TInput input);
    }
    
    public interface IBuild<in TInput, out TOutput>
    {
        TOutput Build(TInput input);
    }
    
    /// <summary>
    /// Implement using your favorite Dependency Injection framework.
    /// </summary>
    public interface IBuildProvider
    {
        IBuild<TInput, TOutput> Get<TInput, TOutput>();
    }
    
    public class Builder : IBuilder
    {
        private readonly IBuildProvider _buildProvider;

        public IBuilderNode<TOutput> Create<TOutput>()
        {
            return new BuilderNode<TOutput>(_buildProvider);
        }

        public Builder(IBuildProvider buildProvider)
        {
            _buildProvider = buildProvider;
        }
    }
    
    public class BuilderNode<TOutput> : IBuilderNode<TOutput>
    {
        private readonly IBuildProvider _buildProvider;

        public TOutput From<TInput>(TInput input)
        {
            var builder = _buildProvider.Get<TInput, TOutput>();
            var result = builder.Build(input);
            return result;
        }

        public BuilderNode(IBuildProvider buildProvider)
        {
            _buildProvider = buildProvider;
        }
    }