Split out strings interner.

src/types/interner.rs

@@ -0,0 +1,71 @@
+use crate::engine::{make_getter, make_setter, FN_GET, FN_SET};
+use crate::{Identifier, ImmutableString};
+#[cfg(feature = "no_std")]
+use std::prelude::v1::*;
+use std::{collections::BTreeMap, ops::AddAssign};
+
+/// _(internals)_ A factory of identifiers from text strings.
+/// Exported under the `internals` feature only.
+///
+/// Since [`SmartString`](https://crates.io/crates/smartstring) is used as [`Identifier`],
+/// this just returns a copy because most identifiers in Rhai are short and ASCII-based.
+///
+/// Property getters and setters are interned separately.
+#[derive(Debug, Clone, Default, Hash)]
+pub struct StringsInterner {
+    /// Property getters.
+    getters: BTreeMap<Identifier, ImmutableString>,
+    /// Property setters.
+    setters: BTreeMap<Identifier, ImmutableString>,
+}
+
+impl StringsInterner {
+    /// Create a new [`IdentifierBuilder`].
+    #[inline]
+    #[must_use]
+    pub fn new() -> Self {
+        Self {
+            getters: BTreeMap::new(),
+            setters: BTreeMap::new(),
+        }
+    }
+    /// Get an identifier from a text string and prefix, adding it to the interner if necessary.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the prefix is not recognized.
+    #[inline]
+    #[must_use]
+    pub fn get(
+        &mut self,
+        prefix: &'static str,
+        text: impl AsRef<str> + Into<Identifier> + Into<ImmutableString>,
+    ) -> ImmutableString {
+        let (dict, mapper) = match prefix {
+            "" => return text.into(),
+            FN_GET => (&mut self.getters, make_getter as fn(&str) -> String),
+            FN_SET => (&mut self.setters, make_setter as fn(&str) -> String),
+            _ => unreachable!("unsupported prefix {}", prefix),
+        };
+
+        if dict.contains_key(text.as_ref()) {
+            self.getters.get(text.as_ref()).expect("exists").clone()
+        } else {
+            let value: ImmutableString = mapper(text.as_ref()).into();
+            let text = text.into();
+            dict.insert(text, value.clone());
+            value
+        }
+    }
+    /// Merge another [`IdentifierBuilder`] into this.
+    #[inline(always)]
+    pub fn merge(&mut self, _other: &Self) {}
+}
+
+impl AddAssign for StringsInterner {
+    #[inline(always)]
+    fn add_assign(&mut self, rhs: Self) {
+        self.getters.extend(rhs.getters.into_iter());
+        self.setters.extend(rhs.setters.into_iter());
+    }
+}