Tips for writing fluent interfaces in C# 3

Question

I'm after some good tips for fluent interfaces in C#. I'm just learning about it myself but keen to hear what others think outside of the articles I am reading. In particular I'm after:

1. when is fluent too much?
2. are there any fluent patterns?
3. what is in C# that makes fluent interfaces more fluent (e.g. extension methods)
4. is a complex fluent interface still a fluent one?
5. refactoring to arrive at a fluent interface or refactoring an existing fluent interface
6. any good examples out there that you have worked with or could recommend?

If you could post one tip or thought, or whatever per post. I want to see how they get voted on, too.

Thank you in advance.

Answer 1

The single biggest challenge I have experienced as a consumer of fluent interfaces is that most of them aren't really fluent intefaces -- instead they are really instances of what I tend to refer to as 'legible interfaces'.

A fluent interface implies that its primary goal is to make it easy to SPEAK it whereas a legible interface implies that its primary goal is to be easy to READ it. Most fluent interfaces only tend to be ridiculously difficult to code with but conversely incredibly easy to READ later by others.

Assert().That().This(actual).Is().Equal().To(expected).     Except().If(x => x.GreaterThan(10)); 

...is alot easier to read later than it is to actually compose in code!

Answer 2

On your 4th point;

Yes I think that a complex fluent interface can still be fluent.

I think fluent interfaces are somewhat of a compromise. (although a good one!) There has been much research into using natural language for programming and generally natural language isn't precise enough to express programs.

Fluent interfaces are constructed so that they write like a programming language, only a small subset of what you can express in a natural language is allowed, but they read like a natural language.

If you look at rhino mocks for example the writing part has been complicated compared to a normal library. I took me longer to learn mostly due to the fluent interface but it makes code a lot easier to read. Because programs are usually written once and read a lot more than once this is a good tradeoff.

So to qualify my point a bit. A fluent interface that's complex to write but easy to read can still be fluent.