Question 1

How do I add a custom date function in Gval?

Accepted Answer

You can extend Gval by defining custom functions; for example, the README shows a date comparator using a custom function, which involves creating a language with the function and parsing expressions with it. This allows handling dates in expressions but requires manual implementation.

Question 2

Is Gval safe for evaluating user-provided expressions?

Accepted Answer

Gval does not include built-in sandboxing or security features, so evaluating untrusted user input can pose risks like infinite loops or resource exhaustion. Developers must implement their own safeguards, such as timeout controls or whitelisting allowed functions.

Question 3

What's the performance difference between parameters and struct accessors in Gval?

Accepted Answer

Using parameters (e.g., from maps) is faster, as benchmarks show single parameter evaluation at ~165 ns/op, while struct accessors are about four times slower due to reflection. For high-throughput scenarios, avoid struct accessors and use custom functions instead.

Question 4

Gval vs expr: which is better for rule engines in Go?

Accepted Answer

Gval excels in extensibility and Go-like syntax, allowing deep customization, while expr may offer more out-of-the-box features and simplicity. Choose Gval if you need a tailored language, but opt for expr if you prefer a more batteries-included approach with less setup.

Question 5

How to parse and reuse expressions in Gval for better performance?

Accepted Answer

Parse expressions using gval.Parse once and store the evaluable result; then reuse it for different parameters. The README emphasizes this reduces compute-intensive parsing overhead, with benchmarks showing parsing times in microseconds versus evaluation in nanoseconds.

Question 6

Can Gval handle JSON arrays and objects natively?

Accepted Answer

Yes, the default language includes JSON arrays and objects as constants, allowing expressions like [1, 2, "foo"] or {"a":1}. However, for complex JSON path queries, you need the external jsonpath library for full support.

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