Making a Go program 42% faster with a one character change

It's quite challenging to provide specific advice without seeing the actual code, but I can offer some general tips that might help you optimize your Go program. Keep in mind that performance improvements can vary based on the specific characteristics of your code and the problem it's solving. Also, a 42% improvement might be optimistic and not always achievable with a one-character change.

Here are some general tips for optimizing Go code:

1. Profiling: Use Go's built-in profiling tools to identify performance bottlenecks. The go tool pprof can help you profile CPU and memory usage. Profiling will give you insights into which parts of your code consume the most resources.
2. Avoid unnecessary allocations: Reducing the number of allocations can significantly improve performance. Use the sync.Pool to reuse objects and minimize garbage collection overhead.
3. Reduce memory copying: If your code involves a lot of copying, consider ways to reduce or eliminate unnecessary copying. This could involve using slices or pointers strategically.
4. Optimize loops: Make sure your loops are as efficient as possible. Minimize branching within loops and consider loop unrolling or vectorization if applicable.
5. Use the right data structures: Choose the most suitable data structures for your specific use case. For example, maps might be faster than slices for certain operations, and vice versa.
6. Parallelism: Leverage Go's concurrency features to parallelize tasks when appropriate. The goroutines and channels can help improve parallelism in your program.
7. Compiler optimizations: Go's compiler is quite good at optimizing code, but you can help it by ensuring that your code is idiomatic and follows best practices.

Remember that before making any optimizations, it's crucial to profile your code to identify the real bottlenecks. Premature optimization without profiling can lead to wasted effort on parts of the code that don't significantly impact performance. Also, consider the trade-off between code readability and optimization – sometimes, making the code more complex for the sake of optimization might not be worth it.