SWIG: Special Handling Of TRUE/FALSE - Good Or Bad?

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SWIG: Special Handling of TRUE/FALSE - Good or Bad?

Let's dive into a discussion about how SWIG (Simplified Wrapper and Interface Generator) handles TRUE and FALSE in C/C++ interfaces. Specifically, we're going to explore whether SWIG should treat these identifiers specially, especially when dealing with languages like Octave and Ruby.

The Curious Case of TRUE and FALSE

In the wild west days of C, before the bool type became standard, many APIs used TRUE and FALSE (all caps, mind you) as substitutes for boolean values. These weren't part of the C standard, but they were widely adopted. Now, SWIG has some special handling for these in certain target languages, notably Octave and Ruby, mapping them to true and false.

Current SWIG Behavior

Currently, SWIG's special treatment primarily affects the autodocumentation of default parameter values. Consider this example:

enum {TRUE = -1, FALSE = 0, UNKNOWN = 1};
int func(int f = TRUE);

SWIG generates Ruby autodoc like this:

 func(int f=true) -> int

Some argue this is misleading. Is it really helpful? The alternative, without special handling, would be:

 func(int f=TRUE) -> int

Which, arguably, is clearer, especially when TRUE is used as a true-like value but isn't exactly true. It shows the actual value being passed, avoiding potential confusion. Think about it, seeing TRUE might prompt a developer to investigate its actual value, leading to a better understanding of the code.

The Ruby Conundrum

Here's where things get even more interesting. Wrapping an API like the one above for Ruby can be tricky. Why? Because Ruby's C API headers contain #define TRUE true. This seemingly makes SWIG's special handling of TRUE almost useless for Ruby. This definition lives in ruby/backward/2/bool.h, which suggests it might be phased out eventually. However, there's no clear mechanism to prevent its inclusion in Ruby 3.3, at least for now.

So, what's the point of SWIG trying to be clever with TRUE when Ruby itself is already defining it as true? It creates potential for conflicts and confusion, rather than clarity.

Why Special Treatment Might Be Problematic

There's a growing sentiment that SWIG should drop the special treatment of TRUE and FALSE. Let's explore why.

Clarity and Accuracy

The primary goal of any documentation or code generation tool should be clarity and accuracy. By blindly converting TRUE to true, SWIG might be obscuring the actual value being used. This is especially true when TRUE is not simply a boolean true but an integer with a specific meaning (e.g., -1 in the example above). Leaving it as TRUE in the documentation preserves the original intent and allows developers to understand the underlying code better.

Consistency

Consistency is key in software development. If SWIG treats TRUE and FALSE differently in different contexts or target languages, it creates confusion and makes the tool harder to use. A more consistent approach would be to simply represent TRUE and FALSE as they are defined in the C/C++ interface, leaving it to the developer to interpret their meaning in the target language.

Avoiding Unnecessary Complexity

Software tools should be as simple as possible, while still being effective. Adding special cases for TRUE and FALSE introduces unnecessary complexity into SWIG's code base. This complexity can lead to bugs and make it harder to maintain the tool in the long run. Removing these special cases would simplify the code and make SWIG more robust.

The Python Precedent

Interestingly, SWIG used to treat TRUE and FALSE specially for Python, even going so far as to include this handling in the generated Python code. However, this was dropped in SWIG 4.0.0 as part of an effort to improve default argument handling. That change happened eight years ago, and, notably, nobody seems to have complained. This suggests that removing the special treatment of TRUE and FALSE is not only feasible but also unlikely to cause significant problems for users.

Lessons Learned

The Python experience teaches us a valuable lesson: sometimes, less is more. By removing the special handling of TRUE and FALSE for Python, SWIG became simpler and more predictable, without sacrificing functionality. This suggests that a similar approach could be successful for other target languages as well.

Arguments for Removing Special Cases

Let's recap the arguments for removing the special cases for TRUE and FALSE in SWIG:

  1. Improved Clarity: Preserves the original meaning of TRUE and FALSE in the documentation.
  2. Increased Consistency: Ensures consistent behavior across different target languages.
  3. Reduced Complexity: Simplifies the SWIG code base and makes it easier to maintain.
  4. Successful Precedent: The Python experience demonstrates that this change is feasible and unlikely to cause problems.

Potential Concerns and Counterarguments

Of course, there might be some concerns about removing the special treatment of TRUE and FALSE. Some might argue that it could break existing code or make it harder to use SWIG with certain libraries. However, these concerns are likely to be minimal, given the Python precedent and the fact that the special handling of TRUE and FALSE is already problematic in some cases (e.g., with Ruby).

Addressing Concerns

Any potential issues can be addressed through careful testing and documentation. Users should be informed about the change and provided with guidance on how to adapt their code if necessary. In most cases, simply removing the special handling of TRUE and FALSE should not cause any problems.

Conclusion: A Case for Simplicity

In conclusion, the evidence suggests that SWIG should indeed drop the special treatment of TRUE and FALSE. It simplifies the tool, improves clarity, and promotes consistency. The Python experience shows that this change is feasible and unlikely to cause significant problems. While there might be some minor concerns, these can be addressed through careful planning and communication.

By embracing simplicity and consistency, SWIG can become an even more powerful and user-friendly tool for wrapping C/C++ interfaces. So, let's ditch the special cases and embrace a more straightforward approach to handling TRUE and FALSE.