add FunctionLoader and StaticFunctionSearcher

an alternative to boxing closures

src/searcher.rs

@@ -250,6 +250,108 @@ impl UserData for StaticClosureSearcher {
     }
 }
 
+/// Like `Searcher`, but with function pointers as `modules` values, to facilitate
+/// setting up an `rlua::Context` with Rust code.
+///
+/// Enables exposing `UserData` types to an `rlua::Context`.
+pub struct FunctionSearcher {
+    /// Functions must accept three parameters:
+    ///
+    /// 1. An `rlua::Context`, which the function body can do what it wants with.
+    ///
+    /// 2. An `rlua::Table` containing globals (i.e. Lua’s `_G`), which can be passed
+    ///    to `Chunk.set_environment()`.
+    ///
+    /// 3. The name of the module to be loaded (`&str`).
+    ///
+    /// Functions must return an `rlua::Result`-wrapped `Function`. This `Function`
+    /// acts as the module loader.
+    modules: HashMap<
+        String,
+        for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+    >,
+
+    globals: RegistryKey,
+}
+
+impl FunctionSearcher {
+    pub fn new(
+        modules: HashMap<
+            String,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+        globals: RegistryKey,
+    ) -> Self {
+        Self { modules, globals }
+    }
+}
+
+impl UserData for FunctionSearcher {
+    fn add_methods<'lua, M>(methods: &mut M)
+    where
+        M: UserDataMethods<'lua, Self>,
+    {
+        methods.add_meta_method(
+            MetaMethod::Call,
+            |lua_ctx: Context<'lua>, this, name: String| {
+                let name = name.as_str();
+                match this.modules.get(name) {
+                    Some(ref function) => Ok(Value::Function(function(
+                        lua_ctx,
+                        lua_ctx.registry_value::<Table>(&this.globals)?,
+                        name,
+                    )?)),
+                    None => Ok(Value::Nil),
+                }
+            },
+        );
+    }
+}
+
+/// Like `FunctionSearcher`, but with `&'static str` keys in `modules`.
+pub struct StaticFunctionSearcher {
+    modules: HashMap<
+        &'static str,
+        for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+    >,
+
+    globals: RegistryKey,
+}
+
+impl StaticFunctionSearcher {
+    pub fn new(
+        modules: HashMap<
+            &'static str,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+        globals: RegistryKey,
+    ) -> Self {
+        Self { modules, globals }
+    }
+}
+
+impl UserData for StaticFunctionSearcher {
+    fn add_methods<'lua, M>(methods: &mut M)
+    where
+        M: UserDataMethods<'lua, Self>,
+    {
+        methods.add_meta_method(
+            MetaMethod::Call,
+            |lua_ctx: Context<'lua>, this, name: String| {
+                let name = name.as_str();
+                match this.modules.get(name) {
+                    Some(ref function) => Ok(Value::Function(function(
+                        lua_ctx,
+                        lua_ctx.registry_value::<Table>(&this.globals)?,
+                        name,
+                    )?)),
+                    None => Ok(Value::Nil),
+                }
+            },
+        );
+    }
+}
+
 /// Extend `rlua::Context` to support `require`ing Lua modules by name.
 pub trait AddSearcher {
     /// Add a `HashMap` of Lua modules indexed by module name to Lua’s
@@ -300,6 +402,24 @@ pub trait AddSearcher {
             >,
         >,
     ) -> Result<()>;
+
+    /// Like `add_searcher`, but with user-provided function for `rlua::Context` setup.
+    fn add_function_searcher(
+        &self,
+        modules: HashMap<
+            String,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+    ) -> Result<()>;
+
+    /// Like `add_function_searcher`, but with `&'static str` keys in `modules`.
+    fn add_static_function_searcher(
+        &self,
+        modules: HashMap<
+            &'static str,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+    ) -> Result<()>;
 }
 
 impl<'a> AddSearcher for Context<'a> {
@@ -392,4 +512,36 @@ impl<'a> AddSearcher for Context<'a> {
             .set(searchers.len()? + 1, searcher)
             .map_err(|e| e.into())
     }
+
+    fn add_function_searcher(
+        &self,
+        modules: HashMap<
+            String,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+    ) -> Result<()> {
+        let globals = self.globals();
+        let searchers: Table = globals.get::<_, Table>("package")?.get("searchers")?;
+        let registry_key = self.create_registry_value(globals)?;
+        let searcher = FunctionSearcher::new(modules, registry_key);
+        searchers
+            .set(searchers.len()? + 1, searcher)
+            .map_err(|e| e.into())
+    }
+
+    fn add_static_function_searcher(
+        &self,
+        modules: HashMap<
+            &'static str,
+            for<'ctx> fn(Context<'ctx>, Table<'ctx>, &str) -> rlua::Result<Function<'ctx>>,
+        >,
+    ) -> Result<()> {
+        let globals = self.globals();
+        let searchers: Table = globals.get::<_, Table>("package")?.get("searchers")?;
+        let registry_key = self.create_registry_value(globals)?;
+        let searcher = StaticFunctionSearcher::new(modules, registry_key);
+        searchers
+            .set(searchers.len()? + 1, searcher)
+            .map_err(|e| e.into())
+    }
 }