IDictionary AddAndReturn extension for fluent interface

Question

What's nice about jQuery, which is a great JavaScript library, is to be able to get the element you are working on as return value. Here is an example of what I am referring to:

$(function() { 
    $("#poo").css("clear", "both").css("margin", "10px");
});

I would like to implement the same for the C# IDictionary interface so that I can write code as follows:

IDictionary<string, string> myDictionary = 
    new Dictionary<string, string>().
        Add("key1", "value1").
        Add("key2", "value2").
        Add("key3", "value3");

So I have created an extension method as below for IDictionary:

public static IDictionary<string, string> AddAndReturn(this IDictionary<string, string> dictionary, string key, string value) {
    dictionary.Add(key, value);
    return dictionary;
}

And now I am able to use it like:

IDictionary<string, string> poo = 
    new Dictionary<string,string>().
        AddAndReturn("key1", "value1").
        AddAndReturn("key2", "value2").
        AddAndReturn("key3", "value3");

I wonder if I am following the right path here.

Is what I am doing a poor man's fluent interface implementation or totally unrelated to that?

Is there any known case for this implementation in C#?

x0n · Accepted Answer · 2011-09-10T18:28:46.433

7

While your implementation pattern is correct (and a common one at that,) your use case is probably not the best choice. ~~Object~~ Collection initializers work for dictionary types too:

var poo =  new Dictionary<string,string> {
        { "key1", "value1" },
        { "key2", "value2" },
        { "key3", "value3" }, // this is permissible
};

The compiler magically turns this into Add(string, string) calls. Btw, the apparently erroneous comma after the last pair is deliberate. The compiler allows this so you can simplify logic in code generators such as T4.

edited Sep 10 '11 at 18:28

answered Sep 10 '11 at 18:18

x0n

51,312
7
89
111

2

Quick bit of terminology: these are *collection initializers*. But yes, this is the idiomatic approach. – Jon Skeet Sep 10 '11 at 18:25
Since C# I-don't-remember-which-version, you can use a special syntax `new Dictionary { ["key"] = "value" }` – Chayim Friedman Jan 28 '21 at 00:16
In fact, collection initializers are available for every type that has a (possibly extension) method named `Add()` – Chayim Friedman Jan 28 '21 at 00:18

score 0 · Answer 2 · edited Jan 28 '21 at 00:13

0

Is there any known case for this implementation in C#?

Regarding this, I would like to add that the StringBuilder.Append() method returns the StringBuilder, making the method chainable, such as:

sb.Append("a").Append("b"). Append("c")

But there aren't many other examples like that in .NET.

edited Jan 28 '21 at 00:13

Pang

9,564
146
81
122

answered Sep 10 '11 at 20:54

Scott Rippey

15,614
5
70
85

IDictionary AddAndReturn extension for fluent interface

2 Answers2