Common Type System—Value Construction

Visual C# Tutorials

.NET Framework Tutorials

Common Type System Type Systems Intro § Types and Objects § Type Unification § Reference, Value Types § Accessibility, Visibility § Type Members § Fields § Methods § Locals Overloading Argument Passing Style Pass-by-Value and Pass-by-Reference Output Parameters Managed Pointers Variable Argument Methods Methods, Subclassing Virtuals, Overriding New Slots Exception Handlers Constructors, Instantiation § Default Constructors Value Construction Constructor Chaining Field Initialization Type Initializers Unhandled Exceptions Properties § Indexers Mixed Mode Accessibility Events Operator Overloading Coercion Subclassing, Polymorphism Styles of Inheritance § Implementation Inheritance Interface Inheritance Abstract Classes Interfaces § Method Dispatch Multiple Inheritance Private Interface Inheritance Private Inheritance Accessibility Interface Reimplementation Abstract and Interface? Sealing Types and Methods Runtime Type Checking Namespaces: Organizing Types § Define a Namespace Namespace Resolution Special Types § Delegates § CTS Support Co- and Contravariance Anonymous Delegates Custom Attributes Enumerations § Flags-Style Limitations Helper Methods Generics § Further Reading §

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© 2006 Wiley Publishing Inc.

Value Construction

Because value types are allocated inline, their default initialization is to zero-out all of their bits without even calling a constructor. This is extremely efficient, avoiding the need to make essentially a method call for each value instantiation. For this reason, C# prohibits creating parameterless constructors for structs. This avoids confusion with the statement new YourValueType(), which is actually compiled into IL that creates a new zeroed out chunk of bits. In C#, you cannot guarantee that value type creation will go through one of your constructors, although this is not entirely obvious immediately.