pub struct Context<'d> { /* private fields */ }
Expand description
Contains the context in which XPath expressions are executed. The context contains functions, variables, and namespace mappings.
Examples
A complete example showing all optional settings.
extern crate sxd_document;
extern crate sxd_xpath;
use std::collections::HashMap;
use sxd_document::parser;
use sxd_xpath::{Factory, Context, Value};
use sxd_xpath::{context, function};
struct Sigmoid;
impl function::Function for Sigmoid {
fn evaluate<'c, 'd>(&self,
_context: &context::Evaluation<'c, 'd>,
args: Vec<Value<'d>>)
-> Result<Value<'d>, function::Error>
{
let mut args = function::Args(args);
args.exactly(1)?;
let val = args.pop_number()?;
let computed = (1.0 + (-val).exp()).recip();
Ok(Value::Number(computed))
}
}
fn main() {
let package = parser::parse("<thing xmlns:ns0='net:brain' ns0:bonus='1' />")
.expect("failed to parse XML");
let document = package.as_document();
let node = document.root().children()[0];
let mut context = Context::new();
context.set_function("sigmoid", Sigmoid);
context.set_variable("t", 2.0);
context.set_namespace("neural", "net:brain");
let xpath = "sigmoid(@neural:bonus + $t)";
let factory = Factory::new();
let xpath = factory.build(xpath).expect("Could not compile XPath");
let xpath = xpath.expect("No XPath was compiled");
let value = xpath.evaluate(&context, node).expect("XPath evaluation failed");
assert_eq!(0.952, (value.number() * 1000.0).trunc() / 1000.0);
}
Note that we are using a custom function (sigmoid
), a variable
($t
), and a namespace (neural:
). The current node is passed to
the evaluate
method and is not the root of the tree but the
top-most element.
Implementations§
source§impl<'d> Context<'d>
impl<'d> Context<'d>
sourcepub fn without_core_functions() -> Self
pub fn without_core_functions() -> Self
No functions, variables or namespaces will be defined.
sourcepub fn set_function<N, F>(&mut self, name: N, function: F)where
N: Into<OwnedQName>,
F: Function + 'static,
pub fn set_function<N, F>(&mut self, name: N, function: F)where
N: Into<OwnedQName>,
F: Function + 'static,
Register a function within the context
sourcepub fn set_variable<N, V>(&mut self, name: N, value: V)where
N: Into<OwnedQName>,
V: Into<Value<'d>>,
pub fn set_variable<N, V>(&mut self, name: N, value: V)where
N: Into<OwnedQName>,
V: Into<Value<'d>>,
Register a variable within the context
sourcepub fn set_namespace(&mut self, prefix: &str, uri: &str)
pub fn set_namespace(&mut self, prefix: &str, uri: &str)
Register a namespace prefix within the context