210 lines
6.3 KiB
Rust
210 lines
6.3 KiB
Rust
//! Module that defines the `Scope` type representing a function call-stack scope.
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use crate::any::{Any, Dynamic};
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use crate::parser::{map_dynamic_to_expr, Expr, Position};
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use std::borrow::Cow;
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/// Type of a variable in the Scope.
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#[derive(Debug, Eq, PartialEq, Hash, Copy, Clone)]
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pub enum VariableType {
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/// Normal variable.
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Normal,
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/// Immutable constant value.
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Constant,
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}
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/// An entry in the Scope.
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pub struct ScopeEntry<'a> {
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/// Name of the variable.
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pub name: Cow<'a, str>,
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/// Type of the variable.
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pub var_type: VariableType,
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/// Current value of the variable.
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pub value: Dynamic,
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/// A constant expression if the initial value matches one of the recognized types.
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pub expr: Option<Expr>,
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}
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/// A type containing information about the current scope.
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/// Useful for keeping state between `Engine` evaluation runs.
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///
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/// # Example
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///
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/// ```rust
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/// # fn main() -> Result<(), rhai::EvalAltResult> {
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/// use rhai::{Engine, Scope};
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///
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/// let mut engine = Engine::new();
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/// let mut my_scope = Scope::new();
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///
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/// engine.eval_with_scope::<()>(&mut my_scope, "let x = 5;")?;
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///
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/// assert_eq!(engine.eval_with_scope::<i64>(&mut my_scope, "x + 1")?, 6);
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/// # Ok(())
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/// # }
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/// ```
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///
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/// When searching for variables, newly-added variables are found before similarly-named but older variables,
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/// allowing for automatic _shadowing_ of variables.
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pub struct Scope<'a>(Vec<ScopeEntry<'a>>);
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impl<'a> Scope<'a> {
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/// Create a new Scope.
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pub fn new() -> Self {
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Self(Vec::new())
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}
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/// Empty the Scope.
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pub fn clear(&mut self) {
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self.0.clear();
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}
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/// Get the number of variables inside the Scope.
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pub fn len(&self) -> usize {
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self.0.len()
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}
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/// Add (push) a new variable to the Scope.
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pub fn push<K: Into<Cow<'a, str>>, T: Any>(&mut self, name: K, value: T) {
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let value = value.into_dynamic();
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// Map into constant expressions
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//let (expr, value) = map_dynamic_to_expr(value, Position::none());
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self.0.push(ScopeEntry {
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name: name.into(),
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var_type: VariableType::Normal,
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value,
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expr: None,
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});
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}
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/// Add (push) a new constant to the Scope.
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///
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/// Constants are immutable and cannot be assigned to. Their values never change.
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/// Constants propagation is a technique used to optimize an AST.
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/// However, in order to be used for optimization, constants must be in one of the recognized types:
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/// `INT` (default to `i64`, `i32` if `only_i32`), `f64`, `String`, `char` and `bool`.
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pub fn push_constant<K: Into<Cow<'a, str>>, T: Any>(&mut self, name: K, value: T) {
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let value = value.into_dynamic();
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// Map into constant expressions
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let (expr, value) = map_dynamic_to_expr(value, Position::none());
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self.0.push(ScopeEntry {
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name: name.into(),
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var_type: VariableType::Constant,
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value,
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expr,
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});
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}
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/// Add (push) a new variable with a `Dynamic` value to the Scope.
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pub(crate) fn push_dynamic<K: Into<Cow<'a, str>>>(
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&mut self,
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name: K,
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var_type: VariableType,
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value: Dynamic,
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) {
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let (expr, value) = map_dynamic_to_expr(value, Position::none());
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self.0.push(ScopeEntry {
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name: name.into(),
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var_type,
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value,
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expr,
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});
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}
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/// Remove (pop) the last variable from the Scope.
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pub fn pop(&mut self) -> Option<(String, VariableType, Dynamic)> {
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self.0.pop().map(
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|ScopeEntry {
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name,
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var_type,
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value,
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..
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}| (name.to_string(), var_type, value),
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)
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}
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/// Truncate (rewind) the Scope to a previous size.
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pub fn rewind(&mut self, size: usize) {
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self.0.truncate(size);
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}
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/// Find a variable in the Scope, starting from the last.
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pub fn get(&self, key: &str) -> Option<(usize, &str, VariableType, Dynamic)> {
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self.0
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.iter()
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.enumerate()
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.rev() // Always search a Scope in reverse order
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.find(|(_, ScopeEntry { name, .. })| name == key)
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.map(
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|(
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i,
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ScopeEntry {
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name,
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var_type,
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value,
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..
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},
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)| (i, name.as_ref(), *var_type, value.clone()),
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)
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}
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/// Get the value of a variable in the Scope, starting from the last.
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pub fn get_value<T: Any + Clone>(&self, key: &str) -> Option<T> {
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self.0
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.iter()
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.enumerate()
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.rev() // Always search a Scope in reverse order
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.find(|(_, ScopeEntry { name, .. })| name == key)
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.and_then(|(_, ScopeEntry { value, .. })| value.downcast_ref::<T>())
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.map(T::clone)
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}
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/// Get a mutable reference to a variable in the Scope.
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pub(crate) fn get_mut(&mut self, name: &str, index: usize) -> &mut Dynamic {
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let entry = self.0.get_mut(index).expect("invalid index in Scope");
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assert_ne!(
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entry.var_type,
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VariableType::Constant,
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"get mut of constant variable"
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);
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assert_eq!(entry.name, name, "incorrect key at Scope entry");
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&mut entry.value
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}
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/// Get a mutable reference to a variable in the Scope and downcast it to a specific type
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#[cfg(not(feature = "no_index"))]
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pub(crate) fn get_mut_by_type<T: Any + Clone>(&mut self, name: &str, index: usize) -> &mut T {
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self.get_mut(name, index)
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.downcast_mut::<T>()
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.expect("wrong type cast")
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}
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/// Get an iterator to variables in the Scope.
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pub fn iter(&self) -> impl Iterator<Item = &ScopeEntry> {
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self.0.iter().rev() // Always search a Scope in reverse order
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}
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}
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impl<'a, K> std::iter::Extend<(K, VariableType, Dynamic)> for Scope<'a>
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where
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K: Into<Cow<'a, str>>,
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{
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fn extend<T: IntoIterator<Item = (K, VariableType, Dynamic)>>(&mut self, iter: T) {
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self.0
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.extend(iter.into_iter().map(|(name, var_type, value)| ScopeEntry {
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name: name.into(),
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var_type,
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value,
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expr: None,
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}));
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}
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}
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