Attributes, Annotations & Decorators

This section is focused on specific examples (like the Deprecated/Obsolete) and how to create your own Attributes, Annotations or Decorators.

For Class Specific Annotations/Decorators like "Override", "Staticmethod" and so on, check the Class Section.

C

// No Standard Attribute System before C23.
// Compilers commonly provide extensions such as GCC attributes.

__attribute__((deprecated))
void old_function()
{
	// ...
}

__attribute__((unused))
static int my_variable;

More Info:

• http://unixwiz.net/techtips/gnu-c-attributes.html

C++

// ------------------------------------
// Deprecated Attribute (since C++14)
// ------------------------------------

// Options:
// [[deprecated]]
// [[deprecated( string message )]]

// Function example
[[deprecated]]
void my_function(void)
{
	// ...
}

// Class example
class [[deprecated("Use another class. This one will be removed next version")]] Myclass
{
	// ...
};

// ------------------------------------
// Custom Attributes
// ------------------------------------

// Standard C++ Doesnt Support Custom Attributes yet

More Info:

• https://en.cppreference.com/w/cpp/language/attributes

C#

// ------------------------------------
// Obsolete Attribute
// ------------------------------------

//[Obsolete]
[Obsolete]
public void MyFunction()
{
	// ...
}

//[Obsolete(string message)]
[Obsolete("Use another class. This one will be removed next version")]
public class MyClass
{
	//...
}

//[Obsolete(string message, bool error)] (error == true means compilation error instead of warning)
[Obsolete("Use another class. This one wont compile", true)]
public class MyClass
{
	//...
}

// ------------------------------------
// Other Standard Attributes
// ------------------------------------

[Serializable]
public class User
{
	// ...
}

[Flags]
public enum FileAccess
{
	Read = 1,
	Write = 2,
	Execute = 4
}

[Conditional("DEBUG")]
public void LogDebug(string message)
{
	// ...
}

// ------------------------------------
// Custom Attributes
// ------------------------------------

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class DocumentationAttribute : Attribute
{
	public string Message { get; }

	public DocumentationAttribute(string message)
	{
		Message = message;
	}
}

[Documentation("Used by the syntax reference examples")]
public class MyClass
{
	// ...
}

Java

// ------------------------------------
// @Deprecated Annotation
// ------------------------------------

// The deprecated message can be documented in the Javadoc @deprecated tag.

/*
* @deprecated Use another method
*/
@Deprecated
public void MyMethod()
{
	// ...
}

// ------------------------------------
// Other Standard Annotations
// ------------------------------------

@Override
public String toString()
{
	return "MyClass";
}

@SuppressWarnings("unchecked")
public void myMethod()
{
	// ...
}

@FunctionalInterface
public interface Operation
{
	int apply(int first, int second);
}

// ------------------------------------
// Custom Annotation
// ------------------------------------

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
public @interface Documentation
{
	String value();
}

@Documentation("Used by the syntax reference examples")
public class MyClass
{
	// ...
}

More Info:

• https://www.codejava.net/java-core/the-java-language/deprecated-annotation-examples
• https://docs.oracle.com/javase/7/docs/technotes/guides/javadoc/deprecation/deprecation.html
• https://en.wikipedia.org/wiki/Java_annotation

Rust

#[derive(Debug, Clone)]
struct User {
	name: String,
}

#[deprecated(note = "Use new_function instead")]
fn old_function() {
	// ...
}

#[allow(dead_code)]
fn helper() {
	// ...
}

Go

// Go has no general attribute/annotation syntax.
// Struct tags are metadata strings used by packages such as encoding/json.

type User struct {
	Name string `json:"name"`
	Age  int    `json:"age,omitempty"`
}

// Compiler directives exist as comments for specific toolchain behavior.
//go:noinline
func myFunction() {
	// ...
}

Javascript

// Decorators are still an experimental feature

// There is a workaround package: https://www.npmjs.com/package/depd

Typescript

// Decorators are still an experimental feature

// There is a workaround package: https://www.npmjs.com/package/depd

Python

# ------------------------------------
# Deprecated Decorator
# ------------------------------------

# from the lib https://pypi.org/project/Deprecated/

from deprecated import deprecated

@deprecated(version='1.2.1', reason="You should use another function")
def some_old_function(x, y):
	return x + y


class SomeClass(object):
	@deprecated(version='1.3.0', reason="This method is deprecated")
	def some_old_method(self, x, y):
		return x + y

# ------------------------------------
# Custom Decorator
# ------------------------------------

from functools import wraps

def trace(function):
	@wraps(function)
	def wrapper(*args, **kwargs):
		print(f"Calling {function.__name__}")
		return function(*args, **kwargs)

	return wrapper

@trace
def add(first, second):
	return first + second