Faux Dictionary Literals in C# 3.0
Posted by Nicholas Blumhardt | September 18, 2007 10:23
Luke Marshall inspired this little, um, gem ;)
If you're enjoying the fresh, functional features in C# 3.0, you might be a little put out by the fact that you can't express dictionaries (maps in C++ parlance, hashes elsewhere) in a single expression. Arrays and lists both have a handy all-in-one initialisation expression so that you can write:
SomeFunction(new[]{ 1, 2, 3 });
Other languages support similar syntax for key-value pairs, e.g. Ruby:
some_function({ :name => 'Nick', :height => 185 })
You can omit the braces in many instances, and v.19 makes the syntax even more succinct.
Well, in C# 3.0 we're not completely out in the cold. There is the interesting new anonymous type declaration that lets us instantiate objects with particular properties in a single statement: There isn't much that we can tell about the object held in
This is enough, however, for an extension method called The code for the magical Disclaimer - this code will make the ToDictionary() method available through every object used in your code - this is one of those abuses of the new extension method feature that you really shouldn't commit! I warned you! :) Posted by Nicholas Blumhardt | September 21, 2007 04:12 I probably should remove your name to protect the (ahem) innocent... hehe Posted by G|oS|co | October 10, 2007 16:42 Be sure to check out Luke's block
"Math Geek Coder" on Blogspot
mathgeekcoder.blogspot.com Posted by Hello, my name is Gudvin, I like yours blog. | November 12, 2007 19:58 Hello, my name is Gudvin, I like yours blog. Posted by Nicholas Blumhardt | December 20, 2007 05:49 The power of the type inferencer surprises me:
var dict = new Dictionary<string,string>(){
{ "A", "This is A" },
{ "B", "A value for B" }
};
This uses the fact that Dictionary implements Add() - the surprise comes from the fact that the KeyValuePair<string,string> item type is used to infer values from { k, v } pairs. Awesome!
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var me = new { Name = "Nick", Height = 185 };
me except that it has the properties Name and Height.ToDictionary() to work some reflective miracles and turn our object into an IDictionary<string,object>...
var props = new { Name = "Nick", Height = 185 }.ToDictionary();
foreach (var prop in props)
Console.WriteLine("{0} = {1}", prop.Key, prop.Value);
ToDictionary() method is below - and, it works on any object.
public static class ToDictionaryExtension
{
public static IDictionary<string, object> ToDictionary(this object o)
{
if (o == null) throw new ArgumentNullException("o");
var dict = new Dictionary<string, object>();
foreach (PropertyInfo pi in o.GetType().GetProperties())
dict[pi.Name] = pi.GetValue(o, null);
return dict;
}
}
Comments
Luke's Blog ...
Hello, my name is Gudvin, I like yours blog.
Dictionary Literals *are* in C#3!
Your Comment
C# Gems
Posted by Luke Marshall | September 20, 2007 19:32
Lookout, I'm a blog inspiration! :) Great article Nick.