Anonymous type property setters

Why do anonymous types not have property setters?

var a = new { Text = "Hello" };
a.Text = "开发者_开发百科World"; //error

Anonymous types are immutable by design.

Anonymous types are meant to hold values, and a type that represents a value should not be mutable.

Also, it would make them unreliable in a dictionary, as the hashcode could change after creation.
Many LINQ methods use Dictionaries, and, especially with delayed evaluation, LINQ with mutable types can lead to subtle mysterious bugs.