Assert Mistakes

Summary:

1. Assert works only in debug builds and is a powerful tool for quickly identifying issues, but improper use can lead to unexpected bugs in release mode.
2. A common mistake junior developers make is including function calls inside an Assert, which can cause those functions not to execute in release mode.
3. To avoid this, use only pure Boolean expressions inside Assert and, if a function call is necessary, clearly separate it as a debug-only function.

Intro

When developing, I always emphasize "Use Assert a lot!" There are various ways to handle errors—exception handling, error codes, TDD, testing, etc.—but Assert is one of the most efficient ways to quickly catch issues during development. In fact, proper use of Assert can cover the basic functionalities of TDD to some extent.

However, there’s a common mistake that junior developers frequently make: including function calls inside an Assert statement. This mistake can lead to problems in release mode, so let’s take a closer look.

The Basics of Assert

Assert has the following key characteristics:

1. It checks a Boolean expression – An Assert statement contains a condition that returns a Boolean value. If the condition is false, code execution stops.
2. It works only in debug builds – In release builds, Assert statements are not executed, meaning they do not impact performance.
3. It helps detect bugs quickly during development – Logical errors can be identified before deployment.

While these advantages make Assert a powerful tool, improper use can cause serious problems.

A Common Mistake Among Junior Developers

Many junior developers make the mistake of calling a function directly inside an Assert:

assert(SomeFunction());

This code works fine in debug mode, but in release mode, SomeFunction() will not be executed, potentially leading to unintended behavior.

Best Practices for Using Assert

To avoid these mistakes, consider following these best practices:

1. Use Only Pure Boolean Expressions Inside Assert

Use variables or simple conditions instead of function calls:

bool bValid = SomeFunction();
assert(bValid);

2. If a Function Call Is Necessary, Ensure It Runs Only in Debug Mode

In such cases, naming the function appropriately helps clarify its purpose:

bool DBG_EnsureValidState();
assert(DBG_EnsureValidState());

Using a DBG_ prefix makes it clear that the function is intended for debug mode only.

3. Keep Important Logic Outside Assert for Release Mode

If a function performs essential initialization or state validation, don’t rely on Assert alone. Keep a separate logic for release mode:

bool bValid = SomeFunction();
assert(bValid);
if (!bValid)
{
    HandleError();
}

Conclusion

Assert is a powerful tool, but incorrect usage can lead to different behavior between debug and release modes. In particular, including function calls inside Assert can cause unexpected bugs in release mode, so this should be avoided at all costs.

This was a mistake I personally made when I was a junior developer, and I’ve seen many others go through the same. So, from now on, build good habits and use Assert effectively!