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Learn how to create a custom assertion function in C+ + 20 that logs errors without using preprocessor directives.
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Implementing assert Without Preprocessor in C+ + 20

In the world of C+ + , runtime assertions play an important role in ensuring that our code behaves as expected. Traditionally, we use assert() which compiles to nothing when the NDEBUG macro is defined. However, there may be times when you want to implement an assertion mechanism without resorting to preprocessor directives. This article explores how to accomplish that in C+ + 20.

The Challenges

When creating a custom assertion function, you want to accomplish the following:

The program should break or terminate if the assertion expression evaluates to false.

You should be able to log the code line where the assertion fails.

In situations where NDEBUG (debugging disabled) is defined, the function should discard the check and any passed expressions.

C+ + 20 introduces several features that can aid us in achieving these goals. However, there’s a fundamental challenge: how can we avoid evaluating the expression when it’s not necessary?

A Possible Solution

Using a Callable

One of the best ways to prevent evaluation of an expression that is passed as an argument is to utilize a callable. This can be a lambda function, allowing you to delay the evaluation until you actually need it. Here’s how you can implement this:

[[See Video to Reveal this Text or Code Snippet]]

Example Usage

To use the assertTrue function, you can pass a lambda that returns the condition you want to assert. Here’s an example of an assertion that always fails:

[[See Video to Reveal this Text or Code Snippet]]

Note on Verbosity

While this approach works effectively to avoid unnecessary evaluations, it may be considered verbose. When calling assertTrue, you must provide a lambda function, which can introduce additional syntax that some may find cumbersome.

Integrating Debugging Macros

In cases where you prefer to keep the condition tight and use a debugging flag, you can enhance the assertion mechanism by wrapping it in debug checks:

[[See Video to Reveal this Text or Code Snippet]]

This allows you to enable or disable assertions easily across your codebase without modifying the assertion logic.

Conclusion

Crafting a custom assertion mechanism in C+ + 20 without using preprocessor directives necessitates a balance between functionality and usability. By utilizing callables and the features introduced in C+ + 20, you can create a flexible assertion function. This approach not only helps maintain the integrity of your code during development but also avoids unnecessary evaluations, particularly in production builds where performance is paramount.

By using this method, you can effectively log and terminate your application based on runtime checks, thus bolstering the robustness of your application.