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use super::SmallCString;
use std::cell::RefCell;
use std::collections::BTreeMap;
/// Maps parameter names to parameter indices.
#[derive(Default, Clone, Debug)]
// BTreeMap seems to do better here unless we want to pull in a custom hash
// function.
pub(crate) struct ParamIndexCache(RefCell<BTreeMap<SmallCString, usize>>);
impl ParamIndexCache {
pub fn get_or_insert_with<F>(&self, s: &str, func: F) -> Option<usize>
where
F: FnOnce(&std::ffi::CStr) -> Option<usize>,
{
let mut cache = self.0.borrow_mut();
// Avoid entry API, needs allocation to test membership.
if let Some(v) = cache.get(s) {
return Some(*v);
}
// If there's an internal nul in the name it couldn't have been a
// parameter, so early return here is ok.
let name = SmallCString::new(s).ok()?;
let val = func(&name)?;
cache.insert(name, val);
Some(val)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_cache() {
let p = ParamIndexCache::default();
let v = p.get_or_insert_with("foo", |cstr| {
assert_eq!(cstr.to_str().unwrap(), "foo");
Some(3)
});
assert_eq!(v, Some(3));
let v = p.get_or_insert_with("foo", |_| {
panic!("shouldn't be called this time");
});
assert_eq!(v, Some(3));
let v = p.get_or_insert_with("gar\0bage", |_| {
panic!("shouldn't be called here either");
});
assert_eq!(v, None);
let v = p.get_or_insert_with("bar", |cstr| {
assert_eq!(cstr.to_str().unwrap(), "bar");
None
});
assert_eq!(v, None);
let v = p.get_or_insert_with("bar", |cstr| {
assert_eq!(cstr.to_str().unwrap(), "bar");
Some(30)
});
assert_eq!(v, Some(30));
}
}
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