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Chapter 9: Anonymous types

Examples

Creating an anonymous type

Since anonymous types are not named, variables of those types must be implicitly typed (var).

var anon = new { Foo = 1, Bar = 2 };
// anon.Foo == 1
// anon.Bar == 2

If the member names are not specified, they are set to the name of the property/variable used to
initialize the object.

int foo = 1;
int bar = 2;
var anon2 = new { foo, bar };
// anon2.foo == 1
// anon2.bar == 2

Note that names can only be omitted when the expression in the anonymous type declaration is a
simple property access; for method calls or more complex expressions, a property name must be
specified.

string foo = "some string";
var anon3 = new { foo.Length };
// anon3.Length == 11
var anon4 = new { foo.Length <= 10 ? "short string" : "long string" };
// compiler error - Invalid anonymous type member declarator.
var anon5 = new { Description = foo.Length <= 10 ? "short string" : "long string" };
// OK

Anonymous vs dynamic

Anonymous types allow the creation of objects without having to explicitly define their types ahead
of time, while maintaining static type checking.

var anon = new { Value = 1 };
Console.WriteLine(anon.Id); // compile time error

Conversely, dynamic has dynamic type checking, opting for runtime errors, instead of compile-time
errors.

dynamic val = "foo";
Console.WriteLine(val.Id); // compiles, but throws runtime error

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