Enable capacity on packages.

src/packages/mod.rs

@@ -53,6 +53,14 @@ pub trait Package {
     #[allow(unused_variables)]
     fn init_engine(engine: &mut Engine) {}
 
+    /// Number of functions expected by the package.
+    ///
+    /// This capacity only acts as a hint. It may not be precise.
+    #[allow(unused_variables)]
+    fn capacity() -> usize {
+        16
+    }
+
     /// Register the package with an [`Engine`].
     ///
     /// # Example
@@ -112,15 +120,17 @@ pub trait Package {
 ///
 /// def_package! {
 ///     /// My super-duper package.
-///     pub MyPackage(module) {
+///     pub MyPackage(module @ 10) {
 ///         // Load a native Rust function.
 ///         module.set_native_fn("my_add", add);
+///     } |> |engine| {
+///         engine.set_custom_operator("@", 160);
 ///     }
 /// }
 /// ```
 #[macro_export]
 macro_rules! def_package {
-    ($($(#[$outer:meta])* $mod:vis $package:ident($lib:ident)
+    ($($(#[$outer:meta])* $mod:vis $package:ident($lib:ident $(@ $capacity:expr)?)
                 $( : $($(#[$base_meta:meta])* $base_pkg:ty),+ )?
                 $block:block
                 $( |> | $engine:ident | $init_engine:block )?
@@ -136,7 +146,7 @@ macro_rules! def_package {
             #[inline]
             fn init($lib: &mut $crate::Module) {
                 $($(
-                    $(#[$base_meta])* { <$base_pkg>::init($lib); }
+                    $(#[$base_meta])* <$base_pkg>::init($lib);
                 )*)*
 
                 $block
@@ -144,7 +154,7 @@ macro_rules! def_package {
             #[inline]
             fn init_engine(_engine: &mut $crate::Engine) {
                 $($(
-                    $(#[$base_meta])* { <$base_pkg>::init_engine(_engine); }
+                    $(#[$base_meta])* <$base_pkg>::init_engine(_engine);
                 )*)*
 
                 $(
@@ -152,6 +162,15 @@ macro_rules! def_package {
                     $init_engine
                 )*
             }
+            #[inline(always)]
+            fn capacity() -> usize {
+                let mut _capacity = 16;
+                $(_capacity = $capacity;)?
+                $($(
+                    $(#[$base_meta])* { _capacity += <$base_pkg>::capacity(); }
+                )*)*
+                _capacity
+            }
         }
 
         impl Default for $package {
@@ -166,7 +185,7 @@ macro_rules! def_package {
             #[inline]
             #[must_use]
             pub fn new() -> Self {
-                let mut module = $crate::Module::new();
+                let mut module = $crate::Module::with_capacity(<Self as $crate::packages::Package>::capacity());
                 <Self as $crate::packages::Package>::init(&mut module);
                 module.build_index();
                 Self(module.into())