Question

If you are writing a function that accepts an argument and you want to make sure the function cannot change the value of the argument, what do you do?

Short answer

Answer: To write a function that cannot change the value of its argument, you can use the concept of immutability. This can be achieved with the following steps: 1. Understand immutability: Immutability refers to the quality of an object whose state cannot be modified after it is created. 2. Consider pass by value or pass by reference: In pass by value, the function cannot change the original value, while in pass by reference, the function can modify the value indirectly. 3. Use different approaches to ensure immutability such as using immutable data types, creating a copy of the object before passing it to the function, or specifying that a function should not modify its arguments (e.g., `const` keyword in C++). 4. In languages like Python, using immutable objects such as strings, integers, and floats ensures that the function cannot change their values.

Step-by-step solution

Understanding Immutability

Immutability refers to the quality of an object whose state cannot be modified after it is created. When we pass arguments to a function, we may want to ensure that the function does not modify their values. This is especially useful when working with data that should remain constant throughout the code execution.

Pass by Value or Pass by Reference

When a function accepts an argument, it can either receive the value of the argument (pass by value) or a reference to the memory location where the argument value is stored (pass by reference). In languages that use pass by value, the function cannot change the original value of the argument. However, in languages that use pass by reference, the function can modify the value of the argument indirectly.

Different Approaches to Ensure Immutability

There are several approaches to ensure immutability: 1. Use immutable data types (e.g., tuples, strings). These data types cannot be modified after they are created, making their values read-only. 2. Use a defensive technique, such as creating a copy of the object before passing it to the function. This allows the function to work with the copy of the data, not the original data. 3. Some programming languages provide features to specify that a function should not modify its arguments (e.g., `const` keyword in C++).

Python Example

In Python, primitive data types (e.g., strings, integers, and floats) are immutable, while some complex data types like lists and dictionaries are mutable. When you pass an immutable object to a function, Python ensures that the function cannot change its value. Here's an example: ```python def modify_string(s): s += " - modified" return s original_string = "Original" modified_string = modify_string(original_string) print("Original string:", original_string) print("Modified string:", modified_string) ``` Output: ``` Original string: Original Modified string: Original - modified ``` In this example, the `modify_string` function cannot change the value of `original_string`, because it is a string, which is an immutable object in Python.