Public Expression::evaluate() returns private Error

[flying-sheep]

the expression crate is private

pub trait Expression: Debug {
    fn evaluate<'a, 'd>(&self, context: &sxd_xpath::EvaluationContext<'a, 'd>)
        -> Result<sxd_xpath::Value<'d>, sxd_xpath::expression::Error>;
}

so if i’m not missing something, this crate is actually unusable for its main purpose: evaluating XPath expressions 😆

[shepmaster]

As I run off to work, I'll point to the integration test, which should exercise it as a user would. I'm sure I need to document something better; perhaps we can figure out what that something is.

[flying-sheep]

surely ok()ping and unwrap()ing everything works for tests/quick&dirty, but in real code error inspection is of course useful.

xpath.evaluate(&context) here returns a Result<Value<'d>, expression::Error>. the expression::Error class is private, so anything except from Result (ok()) and Error trait methods (description()) is lost.

I need to document something better

anything would be a start 😉

but yeah, you can learn well from the integration tests if you find them (what i did)

[shepmaster]

You started by saying

unusable for its main purpose: evaluating XPath expressions

Which would imply that it is impossible to evaluate an expression. Is this true, or are you able to evaluate expressions, but the real problem is that the expression::Error type is private so any useful messages cannot be retrieved? Or are you hoping that the expression::Error type would have more information than the Error trait?

Perhaps I would understand better if you could include a small reproducible example of the code you've written and what you are trying to do.

[flying-sheep]

oh, sorry, of course it’s not impossible to evaluate and stringify the error, just handling it like i do with every other error type:

use sxd_xpath::expression;

enum Error {
    XPath(expression::Error),
    Stuff(SomeOtherError),
}
impl From<expression::Error> for Error {...}
impl From<SomeOtherError> for Error {...}

...

let value = try!(xpath.evaluate(&context));