What are first-class functions and how do they differ across programming languages?

What are first-class functions and how do they differ across programming languages?

First-class functions are functions that can be treated like any other variable. This means they can be assigned to variables, passed as arguments, or returned from other functions. In languages like JavaScript, Python, and Ruby, functions are first-class citizens, while in languages like Java, they are not.

Can you give me examples of first-class functions in JavaScript?

Sure! In JavaScript, you can assign a function to a variable, pass it as an argument, or return it from another function. For example:

const greet = function(name) {
    return `Hello, ${name}!`;
};

const sayHello = greet;
console.log(sayHello('Alice')); // Outputs: Hello, Alice!

How about in Python?

In Python, functions are also first-class citizens. You can define a function and pass it around just like any other object. Here's an example:

def greet(name):
    return f'Hello, {name}!'

say_hello = greet
print(say_hello('Bob'))  # Outputs: Hello, Bob!

Are there any languages where functions are not first-class?

Yes, in languages like Java, functions are not first-class. You typically have to define them within classes, and you can't pass them around as easily as in first-class function languages.