fasteval 0.1.6

Fast evaluation of algebraic expressions
Documentation 
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use crate::error::Error;

use std::collections::BTreeMap;

//---- Types:

pub trait EvalNamespace {
    fn get_cached(   &mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64>;
    fn set_cached(   &mut self, name:String, val:f64);
    fn create_cached(&mut self, name:String, val:f64) -> Result<(),Error>;
    fn clear_cached(&mut self);
}

pub trait Layered {
    fn push(&mut self);
    fn pop(&mut self);
}

pub struct EmptyNamespace;

pub struct CachedFlatNamespace<'a> {
    map:BTreeMap<String,f64>,
    cb :Box<dyn FnMut(&str, Vec<f64>)->Option<f64> + 'a>,  // I think a reference would be more efficient than a Box, but then I would need to use a funky 'let cb=|n|{}; Namespace::new(&cb)' syntax.  The Box results in a super convenient pass-the-cb-by-value API interface.
}

pub struct CachedScopedNamespace<'a> {
    maps:Vec<BTreeMap<String,f64>>,
    cb  :Box<dyn FnMut(&str, Vec<f64>)->Option<f64> + 'a>,
}
pub struct Bubble<'a,'b:'a> {
    ns   :&'a mut CachedScopedNamespace<'b>,
    count:usize,
}


//---- Impls:

#[inline(always)]
fn key_from_nameargs<'a,'b:'a>(keybuf:&'a mut String, name:&'b str, args:&[f64]) -> &'a str {
    if args.is_empty() {
        name
    } else {
        keybuf.clear();
        keybuf.reserve(name.len() + 20*args.len());
        keybuf.push_str(name);
        for f in args {
            keybuf.push_str(" , ");
            keybuf.push_str(&f.to_string());
        };
        keybuf.as_str()
    }
}

impl EvalNamespace for BTreeMap<String,f64> {
    #[inline]
    fn get_cached(&mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64> {
        let key = key_from_nameargs(keybuf, name, &args);
        self.get(key).copied()
    }
    // Think of the 'self' BTreeMap as an alternative to a callback.  When you set/create/clear for other Namespace types,
    // it doesn't modify the callback results -- it modifies the Namespace cache.  Therefore, these become no-ops for this type:
    fn set_cached(&mut self, _name:String, _val:f64) { panic!("cannot set cached value in BTreeMap Namespace"); }
    fn create_cached(&mut self, _name:String, _val:f64) -> Result<(),Error> { panic!("cannot create cached value in BTreeMap Namespace"); }
    fn clear_cached(&mut self) {}
}

impl EvalNamespace for Vec<BTreeMap<String,f64>> {
    #[inline]
    fn get_cached(&mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64> {
        let key = key_from_nameargs(keybuf, name, &args);

        for map in self.iter().rev() {
            if let Some(&val) = map.get(key) { return Some(val); }
        }
        None
    }
    // Think of the 'self' Vec<BTreeMap> as an alternative to a callback.  When you set/create/clear for other Namespace types,
    // it doesn't modify the callback results -- it modifies the Namespace cache.  Therefore, these become no-ops for this type:
    fn set_cached(&mut self, _name:String, _val:f64) { panic!("cannot set cached value in Vec<BTreeMap> Namespace"); }
    fn create_cached(&mut self, _name:String, _val:f64) -> Result<(),Error> { panic!("cannot create cached value in Vec<BTreeMap> Namespace"); }
    fn clear_cached(&mut self) {}
}

impl<F> EvalNamespace for F where F:FnMut(&str,Vec<f64>)->Option<f64> {
    #[inline]
    fn get_cached(&mut self, name:&str, args:Vec<f64>, _keybuf:&mut String) -> Option<f64> {
        self(name,args)
    }
    // This EvalNamespace type doesn't use a cache:
    fn set_cached(&mut self, _name:String, _val:f64) { panic!("cannot set cached value in Uncached CB Namespace"); }
    fn create_cached(&mut self, _name:String, _val:f64) -> Result<(),Error> { panic!("cannot create cached value in Uncached CB Namespace"); }
    fn clear_cached(&mut self) {}
}


impl EvalNamespace for EmptyNamespace {
    #[inline]
    fn get_cached(&mut self, _name:&str, _args:Vec<f64>, _keybuf:&mut String) -> Option<f64> { None }
    fn set_cached(&mut self, _name:String, _val:f64) { panic!("cannot set cached value in EmptyNamespace"); }
    fn create_cached(&mut self, _name:String, _val:f64) -> Result<(),Error> { panic!("cannot create cached value in EmptyNamespace"); }
    fn clear_cached(&mut self) {}
}

impl EvalNamespace for CachedFlatNamespace<'_> {
    fn get_cached(&mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64> {
        let key = key_from_nameargs(keybuf, name, &args);

        if let Some(&val) = self.map.get(key) { return Some(val); }

        match (self.cb)(name,args) {
            Some(val) => {
                self.map.insert(key.to_string(),val);
                Some(val)
            }
            None => None,
        }
    }
    fn set_cached(&mut self, name:String, val:f64) {
        self.map.insert(name, val);
    }
    fn create_cached(&mut self, name:String, val:f64) -> Result<(),Error> {
        if self.map.contains_key(&name) { return Err(Error::AlreadyExists); }
        self.map.insert(name, val);
        Ok(())
    }
    fn clear_cached(&mut self) {
        self.map = BTreeMap::new();
    }
}
impl<'a> CachedFlatNamespace<'a> {
    #[inline]
    pub fn new<F>(cb:F) -> Self where F:FnMut(&str,Vec<f64>)->Option<f64> + 'a {
        CachedFlatNamespace{
            map:BTreeMap::new(),
            cb :Box::new(cb),
        }
    }
}

impl EvalNamespace for CachedScopedNamespace<'_> {
    fn get_cached(&mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64> {
        let key = key_from_nameargs(keybuf, name, &args);

        for map in self.maps.iter().rev() {
            if let Some(&val) = map.get(key) { return Some(val); }
        }

        match (self.cb)(name,args) {
            Some(val) => {
                // I'm using this panic-free 'match' structure for performance:
                match self.maps.last_mut() {
                    Some(m_ref) => { m_ref.insert(key.to_string(),val); }
                    None => (),  // unreachable
                }
                Some(val)
            }
            None => None,
        }
    }
    fn set_cached(&mut self, name:String, val:f64) {
        match self.maps.last_mut() {
            Some(m_ref) => { m_ref.insert(name, val); }
            None => (),  // unreachable
        }
    }
    fn create_cached(&mut self, name:String, val:f64) -> Result<(),Error> {
        match self.maps.last_mut() {
            Some(cur_layer) => {
                if cur_layer.contains_key(&name) { return Err(Error::AlreadyExists); }
                cur_layer.insert(name, val);
            }
            None => return Err(Error::Unreachable),
        };
        Ok(())
    }
    fn clear_cached(&mut self) {
        self.maps = Vec::with_capacity(self.maps.len());  // Assume the future usage will be similar to historical usage.
        self.push();
    }
}
impl Layered for CachedScopedNamespace<'_> {
    #[inline]
    fn push(&mut self) {
        self.maps.push(BTreeMap::new());
    }
    #[inline]
    fn pop(&mut self) {
        self.maps.pop();
    }
}
impl<'a> CachedScopedNamespace<'a> {
    #[inline]
    pub fn new<F>(cb:F) -> Self where F:FnMut(&str,Vec<f64>)->Option<f64> + 'a {
        let mut ns = CachedScopedNamespace{
            maps:Vec::with_capacity(2),
            cb  :Box::new(cb),
        };
        ns.push();
        ns
    }
}

impl Bubble<'_,'_> {
    pub fn new<'a,'b:'a>(ns:&'a mut CachedScopedNamespace<'b>) -> Bubble<'a,'b> {
        Bubble{
            ns,
            count:0,
        }
    }
}
impl Drop for Bubble<'_,'_> {
    fn drop(&mut self) {
        while self.count>0 {
            self.pop();
        }
    }
}
impl EvalNamespace for Bubble<'_,'_> {
    #[inline]
    fn get_cached(&mut self, name:&str, args:Vec<f64>, keybuf:&mut String) -> Option<f64> {
        self.ns.get_cached(name,args,keybuf)
    }
    #[inline]
    fn set_cached(&mut self, name:String, val:f64) {
        self.ns.set_cached(name,val)
    }
    #[inline]
    fn create_cached(&mut self, name:String, val:f64) -> Result<(),Error> {
        self.ns.create_cached(name,val)
    }
    #[inline]
    fn clear_cached(&mut self) {
        self.ns.clear_cached()
    }
}
impl Layered for Bubble<'_,'_> {
    #[inline]
    fn push(&mut self) {
        self.count += 1;
        self.ns.push();
    }
    #[inline]
    fn pop(&mut self) {
        self.ns.pop();
        self.count -= 1;
    }
}



#[cfg(test)]
mod internal_tests {
    use super::*;

    #[test]
    fn bubble() {
        let mut ns = CachedScopedNamespace::new(|_,_| None);
        assert_eq!(ns.maps.len(), 1);
        {
            let mut bub = Bubble::new(&mut ns);  bub.push();
            assert_eq!(bub.ns.maps.len(), 2);
            bub.push();
            assert_eq!(bub.ns.maps.len(), 3);
            bub.push();
            assert_eq!(bub.ns.maps.len(), 4);
            bub.pop();
            assert_eq!(bub.ns.maps.len(), 3);
        }
        assert_eq!(ns.maps.len(), 1);
    }
}