• Article

OpCodes.Box Field

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Converts a value type to an object reference (type O).

Namespace:  System.Reflection.Emit
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Shared ReadOnly Box As OpCode

public static readonly OpCode Box

Remarks

The following table lists the instruction's hexadecimal and Microsoft intermediate language (MSIL) assembly format, along with a brief reference summary:

Format

Assembly Format

Description

8C < T >

box valTypeToken

Convert a value type (of the type specified in valTypeToken) to a true object reference.

The stack transitional behavior, in sequential order, is:

  1. A value type is pushed onto the stack.

  2. The value type is popped from the stack; the box operation is performed.

  3. An object reference to the resulting "boxed" value type is pushed onto the stack.

A value type has two separate representations within the Common Language Infrastructure (CLI):

  • A 'raw' form used when a value type is embedded within another object or on the stack.

  • A 'boxed' form, where the data in the value type is wrapped (boxed) into an object so it can exist as an independent entity.

The box instruction converts the 'raw' (unboxed) value type into an object reference (type O). This is accomplished by creating a new object and copying the data from the value type into the newly allocated object. valTypeToken is a metadata token indicating the type of the value type on the stack.

OutOfMemoryException is thrown if there is insufficient memory to satisfy the request.

TypeLoadException is thrown if the class cannot be found. This is typically detected when MSIL instructions are converted to native code, not at run time.

The following Emit method overload can use the box opcode:

  • ILGenerator.Emit(OpCode, Type)

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.