Question 1

How do I use Expr with my own Go structs?

Accepted Answer

Pass your structs as the environment using expr.Env(), like in the Tweet example, and Expr will automatically infer types and allow field access within expressions without additional configuration.

Question 2

Expr vs. Go template engine: which is better for dynamic rules?

Accepted Answer

Expr excels for logic-heavy expressions with type safety and performance, ideal for business rules, while Go's text/template is better for text generation with simple conditionals, as it lacks Expr's advanced operators and static typing.

Question 3

Can Expr expressions run loops or recursion?

Accepted Answer

No, to ensure termination, Expr does not support recursion or traditional loops; instead, use built-in higher-order functions like map and filter for iterations over collections, as shown in the all() example.

Question 4

Is it safe to evaluate untrusted user input with Expr?

Accepted Answer

Yes, due to its memory-safe design and side-effect-free execution, Expr is built for this use case, preventing code injection and infinite loops, making it a secure choice for configurations like access controls.

Question 5

How to add custom functions to Expr expressions?

Accepted Answer

Define Go functions in your environment map or struct, such as sprintf in the example, and they become callable within expressions, allowing integration with existing Go code without modifications.

Question 6

What's the performance cost of using Expr in hot code paths?

Accepted Answer

Expr is optimized for speed with a bytecode VM, but for extremely latency-sensitive operations, native Go code might be faster; use the provided benchmarks to evaluate trade-offs based on expression complexity.

expr

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