Optimize scope.

src/ast.rs

@@ -2128,7 +2128,7 @@ mod tests {
                 96
             }
         );
-        assert_eq!(size_of::<Scope>(), 288);
+        assert_eq!(size_of::<Scope>(), 160);
         assert_eq!(size_of::<LexError>(), 56);
         assert_eq!(
             size_of::<ParseError>(),

src/scope.rs

@@ -7,7 +7,7 @@ use std::prelude::v1::*;
 use std::{borrow::Cow, iter::Extend};
 
 /// Keep a number of entries inline (since [`Dynamic`] is usually small enough).
-const SCOPE_SIZE: usize = 16;
+const SCOPE_SIZE: usize = 8;
 
 /// Type containing information about the current scope.
 /// Useful for keeping state between [`Engine`][crate::Engine] evaluation runs.
@@ -98,7 +98,7 @@ impl<'a> Scope<'a> {
     pub fn new() -> Self {
         Self {
             values: Default::default(),
-            names: Vec::with_capacity(SCOPE_SIZE),
+            names: Default::default(),
         }
     }
     /// Empty the [`Scope`].