C# Feature – Anonymous types

Overview

Anonymous types create object instances without declaring a formal class, often used in LINQ projections.

Introduced In

C# 3 (2007)

Before

class PersonView { public string Name { get; set; } public int Age { get; set; } }

After

var person = new { Name = "Ada", Age = 42 };

Annotated Example

var query = people.Select(p => new { p.Name, IsAdult = p.Age >= 18 });

Gotchas & Best Practices

• Scope-limited; types are compiler-generated and local to the assembly.
• Great for projections; avoid returning anonymously typed values from public APIs.

Related Features

• Lambda expressions
• LINQ query expressions
• Generics & LINQ

Version Notes

• Works seamlessly with var type inference.