Can Pure Functions Alter Their Input Arguments?
Pure functions are a cornerstone of functional programming, and their behavior is often misunderstood. One common question that arises is whether pure functions can alter their input arguments. In this article, we will delve into this topic and explore the implications of pure functions modifying their inputs.
Understanding Pure Functions
To answer the question, it is essential to first understand what a pure function is. A pure function is a function that, given the same input, will always produce the same output and has no side effects. Side effects refer to any changes made to the state of the program, such as modifying global variables or printing to the console. A pure function is only concerned with the input and output, and nothing else.
Can Pure Functions Alter Their Input Arguments?
The simple answer to the question is no; pure functions cannot alter their input arguments. If a pure function attempts to modify its input, it would violate the principle of purity. However, there is a catch. While pure functions cannot directly alter their input arguments, they can create new data structures that represent the modified values.
Implications of Modifying Inputs
When a pure function creates a new data structure to represent the modified values, it does not affect the original input. This means that the original input remains unchanged, and the function can still be considered pure. However, it is crucial to ensure that the function’s documentation and usage clearly communicate this behavior to avoid confusion.
Examples
Let’s consider a simple example to illustrate this concept. Suppose we have a pure function that squares a number:
“`javascript
function square(x) {
return x x;
}
“`
This function is pure because it only depends on its input and produces the same output for the same input. Now, let’s modify the function to create a new data structure that represents the modified value:
“`javascript
function square(x) {
const result = x x;
return { value: result };
}
“`
In this modified version, the function creates a new object with a `value` property that represents the squared value. The original input `x` remains unchanged, and the function is still considered pure.
Conclusion
In conclusion, pure functions cannot alter their input arguments directly. However, they can create new data structures that represent the modified values while maintaining purity. It is crucial to understand this distinction to design and implement effective functional programs. By adhering to the principles of purity, we can create more predictable and maintainable code.
