Functions

Functions are blocks of reusable code. Here's how different languages define and call functions.

Basic Function Declaration

JavaScript

// Function declaration
function greet(name) {
  return "Hello, " + name;
}

// Arrow function
const greet = (name) => {
  return "Hello, " + name;
};

// Arrow function (shorthand)
const greet = name => "Hello, " + name;

// Function call
greet("John");

PHP

<?php
// Function declaration
function greet($name) {
  return "Hello, " . $name;
}

// With type hints
function add(int $a, int $b): int {
  return $a + $b;
}

// Function call
greet("John");

Rust

// Function declaration
fn greet(name: &str) -> String {
  format!("Hello, {}", name)
}

// Multiple parameters
fn add(a: i32, b: i32) -> i32 {
  a + b  // No semicolon = return
}

// Function call
greet("John");

Go

// Function declaration
func greet(name string) string {
  return "Hello, " + name
}

// Multiple return values
func divide(a, b float64) (float64, error) {
  if b == 0 {
      return 0, errors.New("division by zero")
  }
  return a / b, nil
}

// Function call
greet("John")

Python

# Function declaration
def greet(name):
  return "Hello, " + name

# With type hints
def add(a: int, b: int) -> int:
  return a + b

# Default parameters
def greet(name: str = "World") -> str:
  return f"Hello, {name}"

# Function call
greet("John")

Zig

// Function declaration
fn greet(name: []const u8) ![]const u8 {
  return "Hello, " ++ name;
}

// With error handling
fn divide(a: f64, b: f64) !f64 {
  if (b == 0) return error.DivisionByZero;
  return a / b;
}

// Function call
_ = greet("John");

C#

// Function declaration
public static string Greet(string name)
{
  return "Hello, " + name;
}

// Expression-bodied member
public static string Greet(string name) => "Hello, " + name;

// Default parameters
public static string Greet(string name = "World")
{
  return "Hello, " + name;
}

// Function call
Greet("John");

C++

// Function declaration
std::string greet(const std::string& name) {
  return "Hello, " + name;
}

// Function with default parameter
std::string greet(const std::string& name = "World") {
  return "Hello, " + name;
}

// Function call
greet("John");

C

// Function declaration
char* greet(const char* name) {
  static char result[100];
  sprintf(result, "Hello, %s", name);
  return result;
}

// Function call
greet("John");

Java

// Method declaration
public static String greet(String name) {
  return "Hello, " + name;
}

// Method call
greet("John");

Ruby

# Function declaration
def greet(name)
  "Hello, " + name
end

# Default parameters
def greet(name = "World")
  "Hello, " + name
end

# Function call
greet("John")

Swift

// Function declaration
func greet(name: String) -> String {
  return "Hello, " + name
}

// Shorthand
func greet(name: String) -> String {
  "Hello, " + name
}

// Default parameters
func greet(name: String = "World") -> String {
  "Hello, " + name
}

// Function call
greet(name: "John")

Advanced Function Features

JavaScript

// Default parameters
function greet(name = "World") {
  return "Hello, " + name;
}

// Rest parameters
function sum(...numbers) {
  return numbers.reduce((a, b) => a + b, 0);
}

// Arrow function with this binding
const obj = {
  name: "John",
  greet: function() {
      setTimeout(() => {
          console.log(this.name);
      }, 100);
  }
};

PHP

<?php
// Default parameters
function greet($name = "World") {
  return "Hello, " . $name;
}

// Variadic functions
function sum(...$numbers) {
  return array_sum($numbers);
}

// Type declarations
function process(array $items, callable $callback): array {
  return array_map($callback, $items);
}

Rust

// Closures
let add = |a: i32, b: i32| a + b;

// Higher-order functions
fn apply<F>(f: F, value: i32) -> i32
where
  F: Fn(i32) -> i32,
{
  f(value)
}

// Function pointers
fn double(x: i32) -> i32 {
  x * 2
}
let func: fn(i32) -> i32 = double;

Go

// Variadic functions
func sum(numbers ...int) int {
  total := 0
  for _, n := range numbers {
      total += n
  }
  return total
}

// Function as value
var operation func(int, int) int
operation = func(a, b int) int {
  return a + b
}

Python

# Default parameters
def greet(name="World"):
  return f"Hello, {name}"

# *args and **kwargs
def process(*args, **kwargs):
  print(args)
  print(kwargs)

# Lambda functions
add = lambda a, b: a + b

# Decorators
def my_decorator(func):
  def wrapper():
      print("Before")
      func()
      print("After")
  return wrapper

Zig

// Function pointers
const Operation = fn(i32, i32) i32;

fn add(a: i32, b: i32) i32 {
  return a + b;
}

const op: Operation = add;

// Comptime functions
fn comptimeAdd(comptime a: i32, comptime b: i32) i32 {
  return a + b;
}

C#

// Default parameters
public static string Greet(string name = "World")
{
  return "Hello, " + name;
}

// Params keyword
public static int Sum(params int[] numbers)
{
  return numbers.Sum();
}

// Lambda expressions
Func<int, int, int> add = (a, b) => a + b;

// Action and Func delegates
Action<string> print = name => Console.WriteLine(name);

C++

// Default parameters
std::string greet(const std::string& name = "World") {
  return "Hello, " + name;
}

// Variadic templates (C++11+)
template<typename... Args>
void print(Args... args) {
  ((std::cout << args << " "), ...);
}

// Lambda functions
auto add = [](int a, int b) { return a + b; };

C

// Function pointers
int add(int a, int b) {
  return a + b;
}

int (*operation)(int, int) = add;

// Variadic functions
#include <stdarg.h>
int sum(int count, ...) {
  va_list args;
  va_start(args, count);
  int total = 0;
  for (int i = 0; i < count; i++) {
      total += va_arg(args, int);
  }
  va_end(args);
  return total;
}

Java

// Method overloading
public static int add(int a, int b) {
  return a + b;
}

public static double add(double a, double b) {
  return a + b;
}

// Lambda expressions (Java 8+)
Function<Integer, Integer> square = x -> x * x;

// Method references
Function<String, Integer> length = String::length;

Ruby

# Default parameters
def greet(name = "World")
  "Hello, " + name
end

# Keyword arguments
def create_user(name:, email:, age: 18)
  { name: name, email: email, age: age }
end

# Blocks
[1, 2, 3].each do |n|
  puts n
end

# Procs and lambdas
square = ->(x) { x * x }

Swift

// Default parameters
func greet(name: String = "World") -> String {
  "Hello, " + name
}

// Variadic parameters
func sum(_ numbers: Int...) -> Int {
  numbers.reduce(0, +)
}

// Closures
let add = { (a: Int, b: Int) -> Int in
  return a + b
}

// Trailing closures
numbers.map { $0 * 2 }

Key Takeaways

• Declaration styles -- function (JavaScript, PHP), def (Python, Ruby), fn (Rust, Zig), func (Go, Swift). Arrow functions and lambdas are common in modern languages.
• Parameter passing -- Defaults supported in most; variadic via *args/**kwargs (Python), ... (PHP, Go, Swift, C), params (C#). Zig uses ! for fallible returns.
• Return values -- Go allows multiple returns; Rust uses Result/Option; Zig uses error unions; Python/Ruby allow implicit returns of the last expression.