UZDoom Bug: Parentheses And Anonymous Functions

Hey Doom fans and UZDoom users, have you ever encountered some weird behavior with your custom weapons or mods? Well, buckle up, because we're diving into a peculiar bug in UZDoom that involves anonymous functions and the unexpected allowance of functions without parentheses. This issue can lead to some head-scratching moments and funky gameplay, so let's break it down and see what's going on.

The Root of the Problem: Function Pointers and Anonymous Functions

This bug seems to have emerged with the introduction of function pointers in UZDoom. Function pointers are a powerful feature that allows you to treat functions like variables, passing them around and calling them dynamically. When combined with anonymous functions (functions defined inline, often within a state definition), things can get a little tricky. The core of the problem lies in how UZDoom handles functions without parentheses within these anonymous function contexts. Essentially, the engine allows you to write code where you call a function without the () that usually signal a function call, but it doesn't behave as you'd expect. The function appears to do nothing, which can lead to frustrating debugging sessions.

Imagine you're trying to create a custom pistol in Doom, and you want it to play a specific animation when it's ready to fire. You might write an anonymous function within the weapon's Ready state. This is where the bug rears its ugly head. Instead of the game throwing an error, the code compiles but the function doesn't actually trigger, and your pistol just sits there, perpetually ready. It is a subtle but significant distinction, leading to unexpected outcomes that can be difficult to track down without a solid understanding of how UZDoom interprets your code.

The Bug's Impact: Why This Matters

This bug isn't just a minor inconvenience; it can significantly impact mod development. Let's delve into why this is a concern:

• Unpredictable Behavior: The primary problem is the inconsistent behavior. When a function call without parentheses is allowed, the game doesn't crash, but the intended action of the function doesn't get executed. This is the worst kind of bug, since it doesn't immediately reveal itself, and is a cause of wasting hours trying to figure out why your weapon isn't working as it should.
• Debugging Nightmares: Debugging is much harder. The compiler won't flag these errors, which means you could spend hours poring over your code, only to find the cause is a missing pair of parentheses. This can be very frustrating, especially for beginner modders.
• Code Clarity Issues: The unexpected allowance of these incorrectly formed function calls can make the code less readable. People who may not be familiar with the intricacies of UZDoom might be confused, and have difficulty understanding what the code is meant to do. Clean code is always more maintainable code.

Reproducing the Bug: A Step-by-Step Guide

Reproducing this bug is fairly straightforward. Here's a breakdown of the steps:

1. Download the provided archive: You'll need the ParenthesesAnonFunc.zip file, which contains the necessary files to test the bug. This archive includes a custom weapon, designed to demonstrate the issue.
2. Load the archive: Start UZDoom with the -file command-line argument. This loads the ParenthesesAnonFunc.zip file, which includes your modded assets and code, such as the PistolTest class with A_WeaponReadyTest action. The important aspect here is the Ready state where the action is invoked.
3. Give yourself the weapon: Once the game is running, open the console and type give pistoltest. This command gives you the custom pistol to play with.
4. Test the weapon: Try firing and deselecting the weapon. Observe the behavior and note any unusual happenings. If the function is not working properly, you should see no animation, and you will understand the bug is working.

By following these steps, you can directly observe the issue in action and confirm the bug's presence.

The Code Behind the Issue: A Detailed Example

Let's take a look at the code snippet that highlights this bug. It involves an anonymous function within a state definition: the state is Ready, which triggers A_WeaponReadyTest, which contains the issue of a function without parentheses. You'll see the problematic line where the function is called without parentheses, this is where the bug manifests.

class PistolTest : Pistol
{
 action void A_WeaponReadyTest(int flags = 0)
 {
 A_WeaponReady(flags);
 }

 States {
 Ready:
 PISG A 1
 {
 A_WeaponReadyTest;
 }
 loop;
 }
}

The crucial line here is A_WeaponReadyTest; within the Ready state. The absence of the parentheses after A_WeaponReadyTest allows the compiler to accept it without an error. However, when the game runs, this function call seemingly does nothing, which is the heart of the bug.

Configuration and System Information

While the specific configuration might not play a direct role in triggering this bug, here's the information related to the setup provided:

• UZDoom Version: The issue has been observed in 4.15pre.
• Game: The bug is reproducible in Doom 2.
• Operating System: Tested on Windows 10.

Recommendations and Workarounds

While there isn't a simple fix from a user's perspective, there are ways to mitigate this issue and avoid running into it:

• Always Use Parentheses: The most straightforward workaround is to always include parentheses when calling functions, even in anonymous functions, such as A_WeaponReadyTest();. This ensures the code behaves as expected and avoids confusion. This seems so simple but is the most effective approach.
• Double-Check Your Code: Carefully review your code, particularly around anonymous function calls. This simple act of inspecting the code can prevent a lot of headaches in the long run.
• Test Thoroughly: Always test your modifications and custom content to make sure everything functions correctly. This testing process should uncover issues related to functions that aren't firing properly.
• Report the Issue: If you encounter this bug, report it to the UZDoom developers, along with clear steps to reproduce the issue. Reporting helps the community and promotes the development of a better and more stable version of the engine.

Conclusion: Navigating the UZDoom Bug

This bug, which permits functions without parentheses in anonymous functions, is a subtle but potentially disruptive problem for UZDoom modders. By understanding the bug's root causes, knowing how to reproduce it, and being aware of the possible consequences, you can avoid this trap and develop quality modifications and content for Doom. This is a common situation for most game engines, that can lead to frustration and confusion. By following the recommendations and testing your code thoroughly, you can help ensure that your custom weapons and mods work flawlessly. Keep an eye out for updates and patches from the UZDoom team, and be sure to report any other issues you may encounter.

By staying informed and vigilant, you can navigate these challenges and make the most of your UZDoom modding experience. Keep creating, keep testing, and have fun!

For more in-depth information about UZDoom and ZScript, consider visiting the official ZDoom Wiki. It's an excellent resource for learning more about the engine and scripting language. You can also visit the GZDoom site for updates, and more information about the ZDoom project.