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Questions tagged [reflection]

Reflection is the ability of a program to observe and/or modify its structure and/or behavior at runtime. Reflection is dependent on the supporting programming language - please tag the programming language being used when using this tag.

Overview

Reflection is an ability of a program to perform introspection on itself. This usually involves observing and/or modifying its structure and behavior at runtime.

From a theoretical perspective, reflection relates to the fact that program instructions are stored as data. The distinction between program code and data is a matter of how the information is interpreted, and thus is, in fact, arbitrary. Hence, a program can treat its own code as data and observe or modify it.

Caution should be used when using reflection - the modification of a program's entity during runtime can lead to hard to detect bugs which are generally severe.

Popular questions:

Language-specific implementations

Java:

C#:

Python:

Scala:

See also

24902 questions
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Programmatic equivalent of default(Type)

I'm using reflection to loop through a Type's properties and set certain types to their default. Now, I could do a switch on the type and set the default(Type) explicitly, but I'd rather do it in one line. Is there a programmatic equivalent of…
tags2k
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What are the use(s) for struct tags in Go?

In the Go Language Specification, it mentions a brief overview of tags: A field declaration may be followed by an optional string literal tag, which becomes an attribute for all the fields in the corresponding field declaration. The tags are…
liamzebedee
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How to list all functions in a module?

I have a Python module installed on my system and I'd like to be able to see what functions/classes/methods are available in it. I want to call the help function on each one. In Ruby I can do something like ClassName.methods to get a list of all the…
Chris Gow
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Getting attributes of Enum's value

I would like to know if it is possible to get attributes of the enum values and not of the enum itself? For example, suppose I have the following enum: using System.ComponentModel; // for DescriptionAttribute enum FunkyAttributesEnum { …
Alex K
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Change private static final field using Java reflection

I have a class with a private static final field that, unfortunately, I need to change it at run-time. Using reflection I get this error: java.lang.IllegalAccessException: Can not set static final boolean field Is there any way to change the…
fixitagain
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How to read the value of a private field from a different class in Java?

I have a poorly designed class in a 3rd-party JAR and I need to access one of its private fields. For example, why should I need to choose private field is it necessary? class IWasDesignedPoorly { private Hashtable…
Frank Krueger
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How do I get the path and name of the python file that is currently executing?

I have scripts calling other script files but I need to get the filepath of the file that is currently running within the process. For example, let's say I have three files. Using execfile: script_1.py calls script_2.py. In turn, script_2.py…
Ray
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Getting the name of the currently executing method

Is there a way to get the name of the currently executing method in Java?
Omar Kooheji
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What is the difference between instanceof and Class.isAssignableFrom(...)?

Which of the following is better? a instanceof B or B.class.isAssignableFrom(a.getClass()) The only difference that I know of is, when 'a' is null, the first returns false, while the second throws an exception. Other than that, do they always give…
Megamug
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Get class name of object as string in Swift

Getting the classname of an object as String using: object_getClassName(myViewController) returns something like this: _TtC5AppName22CalendarViewController I am looking for the pure version: "CalendarViewController". How do I get a cleaned up…
Bernd
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Test if object implements interface

What is the simplest way of testing if an object implements a given interface in C#? (Answer to this question in Java)
JoshRivers
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Open Source Alternatives to Reflector?

Just to ask if anyone knows of an open source alternative to RedGate's Reflector? I'm interested in checking out how a tool similar to Reflector actually works. Note, if you know of a free but not open source alternative to Reflector, you can…
Tangiest
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Is a Java string really immutable?

We all know that String is immutable in Java, but check the following code: String s1 = "Hello World"; String s2 = "Hello World"; String s3 = s1.substring(6); System.out.println(s1); // Hello World System.out.println(s2); // Hello World …
Darshan Patel
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How can I get a list of all classes within current module in Python?

I've seen plenty of examples of people extracting all of the classes from a module, usually something like: # foo.py class Foo: pass # test.py import inspect import foo for name, obj in inspect.getmembers(foo): if inspect.isclass(obj): …
mcccclean
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How do I check if a type is a subtype OR the type of an object?

To check if a type is a subclass of another type in C#, it's easy: typeof (SubClass).IsSubclassOf(typeof (BaseClass)); // returns true However, this will fail: typeof (BaseClass).IsSubclassOf(typeof (BaseClass)); // returns false Is there any way…
Daniel T.
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