In the .NET Framework architecture, .NET metadata refers to certain data structures embedded within the Common Intermediate Language code that describes the high-level structure of the code.

Metadata describes all classes and class members that are defined in the assembly, and the classes and class members that the current assembly will call from another assembly. The metadata for a method contains the complete description of the method, including the class, the return type and all of the method parameters.

A .NET language compiler will generate the metadata and store this in the assembly containing the CIL. When the CLR executes CIL it will check to make sure that the metadata of the called method is the same as the metadata that is stored in the calling method. This ensures that a method can only be called with exactly the right number of parameters and exactly the right parameter types.

Assemblies contain tables of metadata. These tables are described by the CIL specification. The metadata tables will have zero or more entries and the position of an entry determines its index. When CIL code uses metadata it does so through a metadata token. Learn more of this with the houston .net developer.

This is a 32-bit value where the top 8 bits identify the appropriate metadata table, and the remaining 24 bits give the index of the metadata in the table. The Framework SDK contains a sample called metainfo that will list the metadata tables in an assembly, however, this information is rarely of use to a developer. Metadata in an assembly may be viewed using the ILDASM tool provided by the .NET Framework SDK.

Reflection is the API used to read .NET metadata. The reflection API provides a logical view of metadata rather than the literal view provided by tools like metainfo. Reflection in version 1.1 of the .NET framework can be used to inspect the descriptions of classes and their members, and invoke methods. Visit the houston .net developer to learn more about Reflection.

However, it does not allow runtime access to the CIL for a method. Version 2.0 of the framework allows the CIL for a method to be obtained. More information can be found with the houston .net developer.