Why Should Programmers Avoid Global Variables?

Why Global Variables Should Be Avoided in Programming

In the realm of programming, the use of global variables is often frowned upon. But what's the underlying reason for this skepticism?

Global Variables: A Double-Edged Sword

Global variables are accessible from anywhere within a program, making them convenient for storing shared data. However, this convenience comes at a cost: it introduces hidden side effects into functions.

The Dangers of Hidden Side Effects

When a function modifies a global variable, it creates side effects that can be difficult to detect and debug. This is because other functions in the program can also access and modify the same global variable, leading to unexpected outcomes.

As a result, using global variables can increase the complexity of the code, making it more challenging to maintain and ensure its correctness. This can ultimately lead to spaghetti code, where the connections between code elements become tangled and difficult to understand.

Exceptions: Global Constants vs. Global Variables

It's important to note that global constants are conceptually different from global variables. Global constants are assigned values that never change, while global variables can be modified at runtime. In Python, global constants are typically written in all-uppercase letters.

When to Consider Global State

While global variables are generally discouraged, there are some cases where global state may be necessary. For example, it can be useful for caching, memoization, or maintaining consistent data shared across different parts of a program. However, it's essential to use global state sparingly and carefully to avoid introducing unwanted side effects.

Additional Resources

For further insights into why global variables can be problematic and for additional learning on functional programming, consider the following resources:

• Global Variables Are Bad - Wiki Wiki Web
• Why is Global State so Evil? - Software Engineering Stack Exchange
• Are Global Variables Bad?
• Side Effect (Computer Science) - Wikipedia
• Functional Programming - Wikipedia

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