Why do some lines start with a period in C# during object creation?

Question

Referring to the example below, what is going on when the new logger is created? Several lines start with a ".". I'm guessing this is object initialization, but it doesn't seem like normal constructor arguments.

What is this syntax doing?

If you delete the whitespace (which is largely ignored by the compiler), do you understand the line then? — Hans Keﬆing, Jan 09 '20 at 15:52
Given the fact that the `;` terminates your line, and the fact that you already have `.MinimumLevel.Verbose()` as an example it should be relatively apparent to you. No? It is just one long line of code split on several lines. — Andrew Truckle, Jan 09 '20 at 15:54
@HansKeﬆing I understand that whitespace is ignored, but it seems like an odd way to create an object. Why not just have input arguments for each setting? — Izzo, Jan 09 '20 at 15:58
See also: https://softwareengineering.stackexchange.com/questions/69519/when-to-go-fluent-in-c, https://stackoverflow.com/questions/2084503/whats-a-fluent-interface, https://stackoverflow.com/questions/17937755/what-is-the-difference-between-a-fluent-interface-and-the-builder-pattern/17937946 — canton7, Jan 09 '20 at 16:00

score 8 · Accepted Answer · answered Jan 09 '20 at 15:52

8

This is just a chain of methods and properties. You can take:

something.A.B().C.D().E.F();

And add newlines to write it as:

something
    .A.B()
    .C.D()
    .E.F();

More generally, this style of method chaining to configure an object is called a Fluent Interface.

answered Jan 09 '20 at 15:52

canton7

37,633
3
64
77

You learnt me how it was called. Thank you ! Just adding [this post](https://assist-software.net/blog/design-and-implement-fluent-interface-pattern-c) in my comment as it illustrates with an example – WilliamW Jan 09 '20 at 15:59
Why is it necessary to create an object this way though? Why not just input arguments for each setting? – Izzo Jan 09 '20 at 15:59
@Izzo The designer of that interface decided that it was a nicer (i.e. cleaner, easier to read and write) way of configuring the builder than calling individual methods or having lots of input arguments. I've added some links to a comment on your OP. – canton7 Jan 09 '20 at 16:01

score 2 · Answer 2 · answered Jan 09 '20 at 15:53

The object is created here:

new LoggerConfiguration()

The next part is accessing a property on the new object:

.MinimumLevel

Followed by a method call on the object referenced by that property:

.Verbose()

And so on.

The entire statement represents a single expression, the result of which is assigned to the variable logger.

Why do some lines start with a period in C# during object creation?

2 Answers2