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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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What is reflection and why is it useful?

What is reflection, and why is it useful? I'm particularly interested in Java, but I assume the principles are the same in any language.
Lehane
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Calling a function of a module by using its name (a string)

How do I call a function, using a string with the function's name? For example: import foo func_name = "bar" call(foo, func_name) # calls foo.bar()
ricree
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How do I use reflection to call a generic method?

What's the best way to call a generic method when the type parameter isn't known at compile time, but instead is obtained dynamically at runtime? Consider the following sample code - inside the Example() method, what's the most concise way to invoke…
Bevan
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How to create a generic array in Java?

Due to the implementation of Java generics, you can't have code like this: public class GenSet { private E a[]; public GenSet() { a = new E[INITIAL_ARRAY_LENGTH]; // error: generic array creation } } How can I implement…
tatsuhirosatou
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Get property value from string using reflection

I am trying implement the Data transformation using Reflection1 example in my code. The GetSourceValue function has a switch comparing various types, but I want to remove these types and properties and have GetSourceValue get the value of the…
pedrofernandes
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How do I get the path of the assembly the code is in?

Is there a way to get the path for the assembly in which the current code resides? I do not want the path of the calling assembly, just the one containing the code. Basically my unit test needs to read some xml test files which are located…
George Mauer
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How to create a new object instance from a Type

One may not always know the Type of an object at compile-time, but may need to create an instance of the Type. How do you get a new object instance from a Type?
tags2k
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11 answers

How to get the list of properties of a class?

How do I get a list of all the properties of a class?
Sukesh
767
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23 answers

How do I invoke a Java method when given the method name as a string?

If I have two variables: Object obj; String methodName = "getName"; Without knowing the class of obj, how can I call the method identified by methodName on it? The method being called has no parameters, and a String return value. It's a getter for…
brasskazoo
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How to determine if a type implements an interface with C# reflection

Does reflection in C# offer a way to determine if some given System.Type type models some interface? public interface IMyInterface {} public class MyType : IMyInterface {} // should yield 'true' typeof(MyType)./* ?????…
Yippie-Ki-Yay
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C# getting its own class name

If I have a class called MyProgram, is there a way of retrieving "MyProgram" as a string?
deltanovember
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656
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19 answers

Getting all types that implement an interface

Using reflection, how can I get all types that implement an interface with C# 3.0/.NET 3.5 with the least code, and minimizing iterations? This is what I want to re-write: foreach (Type t in this.GetType().Assembly.GetTypes()) if (t is…
juan
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Get generic type of class at runtime

How can I achieve this? public class GenericClass { public Type getMyType() { //How do I return the type of T? } } Everything I have tried so far always returns type Object rather than the specific type used.
Glenn
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Can you find all classes in a package using reflection?

Is it possible to find all classes or interfaces in a given package? (Quickly looking at e.g. Package, it would seem like no.)
Jonik
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Checking if a variable is defined?

How can I check whether a variable is defined in Ruby? Is there an isset-type method available?
readonly
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