You are previewing Programming F# 3.0, 2nd Edition.

Programming F# 3.0, 2nd Edition

Cover of Programming F# 3.0, 2nd Edition by Chris Smith Published by O'Reilly Media, Inc.
  1. Programming F# 3.0
  2. Preface
    1. Introducing F#
    2. Who This Book Is For
    3. What You Need to Get Going
    4. How the Book Is Organized
      1. Part I
      2. Part II
      3. Part III
    5. Part IV
    6. Conventions Used in This Book
    7. Using Code Examples
    8. Safari® Books Online
    9. I’d Like to Hear from You
    10. Acknowledgments
  3. I. Multiparadigm Programming
    1. 1. Introduction to F#
      1. Getting to Know F#
      2. Visual Studio 11
      3. F# Interactive
      4. Managing F# Source Files
    2. 2. Fundamentals
      1. Primitive Types
      2. Comparison and Equality
      3. Functions
      4. Core Types
      5. Organizing F# Code
    3. 3. Functional Programming
      1. Understanding Functions
      2. Pattern Matching
      3. Discriminated Unions
      4. Records
      5. Lazy Evaluation
      6. Sequences
      7. Queries
    4. 4. Imperative Programming
      1. Understanding Memory in .NET
      2. Changing Values
      3. Units of Measure
      4. Arrays
      5. Mutable Collection Types
      6. Looping Constructs
      7. Exceptions
    5. 5. Object-Oriented Programming
      1. Programming with Objects
      2. Understanding System.Object
      3. Understanding Classes
      4. Methods and Properties
      5. Inheritance
    6. 6. .NET Programming
      1. The .NET Platform
      2. Interfaces
      3. Object Expressions
      4. Extension Methods
      5. Extending Modules
      6. Enumerations
      7. Structs
  4. II. Programming F#
    1. 7. Applied Functional Programming
      1. Active Patterns
      2. Using Modules
      3. Mastering Lists
      4. Tail Recursion
      5. Programming with Functions
      6. Functional Patterns
      7. Functional Data Structures
    2. 8. Applied Object-Oriented Programming
      1. Operators
      2. Generic Type Constraints
      3. Delegates and Events
      4. Events
    3. 9. Asynchronous and Parallel Programming
      1. Working with Threads
      2. Asynchronous Programming
      3. Asynchronous Workflows
      4. Parallel Programming
      5. Task Parallel Library
    4. 10. Scripting
      1. F# Script Files
      2. Directives
      3. F# Script Recipes
    5. 11. Data Processing
      1. Indexing
      2. Querying
  5. III. Extending the F# Language
    1. 12. Reflection
      1. Attributes
      2. Type Reflection
      3. Dynamic Instantiation
      4. Using Reflection
    2. 13. Computation Expressions
      1. Toward Computation Expressions
      2. Computation Expression Builders
      3. Custom Computation Expression Builders
    3. 14. Quotations
      1. Quotation Basics
      2. Generating Quotation Expressions
    4. 15. Type Providers
      1. Typed Data Versus Typed Languages
      2. Type Providers
  6. IV. Appendixes
    1. A. Overview of .NET Libraries
      1. Visualization
      2. Data Processing
      3. Storing Data
    2. B. F# Interop
      1. .NET Interop
      2. Unmanaged Interop
  7. Index
  8. About the Author
  9. Colophon
  10. Copyright

Chapter 12. Reflection

We have covered almost all of the raw syntax of F#, and the programming paradigms it enables. In this chapter, you won’t learn any new capabilities of the F# language per se; instead you will learn how to harness the .NET Reflection APIs.

Reflection allows you to access the runtime metadata information about executing code. Metadata can be raw type information, such as the methods a class has, or it can come in the form of attributes, which are programmer-supplied code annotations.

The most common usage of .NET reflection is for metaprogramming, which is writing programs that reason about themselves, or modify themselves, such as those that can load plug-ins to add new functionality at runtime. In other words, allowing other developers to extend your application without them needing to have access to the source code.

But before you can do full-on metaprogramming, you must first understand how to annotate code to provide metadata.


Attributes are a form of metadata you can attach to assemblies, methods, parameters, and so on. These annotations can then be inspected at runtime using reflection, which we get to later in this chapter. The F# compiler will recognize attributes as well; in fact, you have been using attributes for a while now to provide hints for how to compile your code.

Recall from Chapter 5 that in order to mark a class as abstract, you need to provide the [<Abstract>] attribute to the type declaration. When the F# compiler sees that attribute, ...

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