Introduce a `Class` map (#3315)

* Improve `Class` and `ClassBuilder` ergonomics

* Fix tests

* Apply review

* Fix docs

boa_engine/src/builtins/intl/segmenter/segments.rs

@@ -25,11 +25,7 @@ impl IntrinsicObject for Segments {
 
         BuiltInBuilder::with_intrinsic::<Self>(realm)
             .static_method(Self::containing, js_string!("containing"), 1)
-            .static_method(
-                Self::iterator,
-                (JsSymbol::iterator(), js_string!("[Symbol.iterator]")),
-                0,
-            )
+            .static_method(Self::iterator, JsSymbol::iterator(), 0)
             .build();
     }
 

boa_engine/src/builtins/iterable/mod.rs

@@ -161,11 +161,7 @@ impl IntrinsicObject for Iterator {
         let _timer = Profiler::global().start_event("Iterator Prototype", "init");
 
         BuiltInBuilder::with_intrinsic::<Self>(realm)
-            .static_method(
-                |v, _, _| Ok(v.clone()),
-                (JsSymbol::iterator(), js_string!("[Symbol.iterator]")),
-                0,
-            )
+            .static_method(|v, _, _| Ok(v.clone()), JsSymbol::iterator(), 0)
             .build();
     }
 
@@ -187,14 +183,7 @@ impl IntrinsicObject for AsyncIterator {
         let _timer = Profiler::global().start_event("AsyncIteratorPrototype", "init");
 
         BuiltInBuilder::with_intrinsic::<Self>(realm)
-            .static_method(
-                |v, _, _| Ok(v.clone()),
-                (
-                    JsSymbol::async_iterator(),
-                    js_string!("[Symbol.asyncIterator]"),
-                ),
-                0,
-            )
+            .static_method(|v, _, _| Ok(v.clone()), JsSymbol::async_iterator(), 0)
             .build();
     }
 

boa_engine/src/builtins/regexp/mod.rs

@@ -95,31 +95,11 @@ impl IntrinsicObject for RegExp {
             .method(Self::test, js_string!("test"), 1)
             .method(Self::exec, js_string!("exec"), 1)
             .method(Self::to_string, js_string!("toString"), 0)
-            .method(
-                Self::r#match,
-                (JsSymbol::r#match(), js_string!("[Symbol.match]")),
-                1,
-            )
-            .method(
-                Self::match_all,
-                (JsSymbol::match_all(), js_string!("[Symbol.matchAll]")),
-                1,
-            )
-            .method(
-                Self::replace,
-                (JsSymbol::replace(), js_string!("[Symbol.replace]")),
-                2,
-            )
-            .method(
-                Self::search,
-                (JsSymbol::search(), js_string!("[Symbol.search]")),
-                1,
-            )
-            .method(
-                Self::split,
-                (JsSymbol::split(), js_string!("[Symbol.split]")),
-                2,
-            )
+            .method(Self::r#match, JsSymbol::r#match(), 1)
+            .method(Self::match_all, JsSymbol::match_all(), 1)
+            .method(Self::replace, JsSymbol::replace(), 2)
+            .method(Self::search, JsSymbol::search(), 1)
+            .method(Self::split, JsSymbol::split(), 2)
             .accessor(
                 js_string!("hasIndices"),
                 Some(get_has_indices),

boa_engine/src/builtins/string/mod.rs

@@ -78,8 +78,6 @@ impl IntrinsicObject for String {
     fn init(realm: &Realm) {
         let _timer = Profiler::global().start_event(std::any::type_name::<Self>(), "init");
 
-        let symbol_iterator = JsSymbol::iterator();
-
         let trim_start = BuiltInBuilder::callable(realm, Self::trim_start)
             .length(0)
             .name(js_string!("trimStart"))
@@ -150,11 +148,7 @@ impl IntrinsicObject for String {
             .method(Self::match_all, js_string!("matchAll"), 1)
             .method(Self::replace, js_string!("replace"), 2)
             .method(Self::replace_all, js_string!("replaceAll"), 2)
-            .method(
-                Self::iterator,
-                (symbol_iterator, js_string!("[Symbol.iterator]")),
-                0,
-            )
+            .method(Self::iterator, JsSymbol::iterator(), 0)
             .method(Self::search, js_string!("search"), 1)
             .method(Self::at, js_string!("at"), 1);
 

boa_engine/src/class.rs

@@ -8,10 +8,11 @@
 //! #    class::{Class, ClassBuilder},
 //! #    Context, JsResult, JsValue,
 //! #    JsArgs,
+//! #    js_string,
 //! # };
 //! # use boa_gc::{Finalize, Trace};
 //! #
-//! // This does not have to be an enum it can also be a struct.
+//! // Can also be a struct containing `Trace` types.
 //! #[derive(Debug, Trace, Finalize)]
 //! enum Animal {
 //!     Cat,
@@ -26,8 +27,8 @@
 //!     // We set the length to `1` since we accept 1 arguments in the constructor.
 //!     const LENGTH: usize = 1;
 //!
-//!     // This is what is called when we do `new Animal()`
-//!     fn constructor(_this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self> {
+//!     // This is what is called when we do `new Animal()` to construct the inner data of the class.
+//!     fn make_data(_this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self> {
 //!         // This is equivalent to `String(arg)`.
 //!         let kind = args.get_or_undefined(0).to_string(context)?;
 //!
@@ -43,7 +44,7 @@
 //!     /// This is where the object is initialized.
 //!     fn init(class: &mut ClassBuilder) -> JsResult<()> {
 //!         class.method(
-//!             "speak",
+//!             js_string!("speak"),
 //!             0,
 //!             NativeFunction::from_fn_ptr(|this, _args, _ctx| {
 //!                 if let Some(object) = this.as_object() {
@@ -66,83 +67,68 @@
 //! [class-trait]: ./trait.Class.html
 
 use crate::{
+    context::intrinsics::StandardConstructor,
     error::JsNativeError,
-    js_string,
     native_function::NativeFunction,
-    object::{ConstructorBuilder, JsFunction, JsObject, NativeObject, ObjectData, PROTOTYPE},
+    object::{
+        ConstructorBuilder, FunctionBinding, JsFunction, JsObject, NativeObject, ObjectData,
+        PROTOTYPE,
+    },
     property::{Attribute, PropertyDescriptor, PropertyKey},
     Context, JsResult, JsValue,
 };
 
 /// Native class.
 pub trait Class: NativeObject + Sized {
-    /// The binding name of the object.
+    /// The binding name of this class.
     const NAME: &'static str;
-    /// The amount of arguments the class `constructor` takes, default is `0`.
+    /// The amount of arguments this class' constructor takes. Default is `0`.
     const LENGTH: usize = 0;
-    /// The attributes the class will be binded with, default is `writable`, `enumerable`, `configurable`.
+    /// The property attributes of this class' constructor in the global object.
+    /// Default is `writable`, `enumerable`, `configurable`.
     const ATTRIBUTES: Attribute = Attribute::all();
 
-    /// The constructor of the class.
-    fn constructor(this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self>;
+    /// Creates the internal data for an instance of this class.
+    ///
+    /// This method can also be called the "native constructor" of this class.
+    fn make_data(this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self>;
 
-    /// Initializes the internals and the methods of the class.
+    /// Initializes the properties and methods of this class.
     fn init(class: &mut ClassBuilder<'_, '_>) -> JsResult<()>;
-}
-
-/// This is a wrapper around `Class::constructor` that sets the internal data of a class.
-///
-/// This is automatically implemented, when a type implements `Class`.
-pub trait ClassConstructor: Class {
-    /// The raw constructor that matches the `NativeFunction` signature.
-    fn raw_constructor(
-        this: &JsValue,
-        args: &[JsValue],
-        context: &mut Context<'_>,
-    ) -> JsResult<JsValue>
-    where
-        Self: Sized;
-}
 
-impl<T: Class> ClassConstructor for T {
-    fn raw_constructor(
-        this: &JsValue,
+    /// Creates a new [`JsObject`] with its internal data set to the result of calling `Self::make_data`.
+    ///
+    /// # Note
+    ///
+    /// This will throw an error if this class is not registered in the context's active realm.
+    /// See [`Context::register_global_class`].
+    ///
+    /// # Warning
+    ///
+    /// Overriding this method could be useful for certain usages, but incorrectly implementing this
+    /// could lead to weird errors like missing inherited methods or incorrect internal data.
+    fn construct(
+        new_target: &JsValue,
         args: &[JsValue],
         context: &mut Context<'_>,
-    ) -> JsResult<JsValue>
-    where
-        Self: Sized,
-    {
-        if this.is_undefined() {
+    ) -> JsResult<JsObject> {
+        if new_target.is_undefined() {
             return Err(JsNativeError::typ()
                 .with_message(format!(
                     "cannot call constructor of native class `{}` without new",
-                    T::NAME
+                    Self::NAME
                 ))
                 .into());
         }
 
-        let class = context.global_object().get(js_string!(T::NAME), context)?;
-        let JsValue::Object(ref class_constructor) = class else {
-            return Err(JsNativeError::typ()
-                .with_message(format!(
-                    "invalid constructor for native class `{}` ",
-                    T::NAME
-                ))
-                .into());
-        };
+        let class = context.get_global_class::<Self>().ok_or_else(|| {
+            JsNativeError::typ().with_message(format!(
+                "could not find native class `{}` in the map of registered classes",
+                Self::NAME
+            ))
+        })?;
 
-        let JsValue::Object(ref class_prototype) = class_constructor.get(PROTOTYPE, context)?
-        else {
-            return Err(JsNativeError::typ()
-                .with_message(format!(
-                    "invalid default prototype for native class `{}`",
-                    T::NAME
-                ))
-                .into());
-        };
-
-        let prototype = this
+        let prototype = new_target
             .as_object()
             .map(|obj| {
                 obj.get(PROTOTYPE, context)
@@ -150,15 +136,15 @@ impl<T: Class> ClassConstructor for T {
             })
             .transpose()?
             .flatten()
-            .unwrap_or_else(|| class_prototype.clone());
+            .unwrap_or_else(|| class.prototype());
 
-        let native_instance = Self::constructor(this, args, context)?;
-        let object_instance = JsObject::from_proto_and_data_with_shared_shape(
+        let data = Self::make_data(new_target, args, context)?;
+        let instance = JsObject::from_proto_and_data_with_shared_shape(
             context.root_shape(),
             prototype,
-            ObjectData::native_object(native_instance),
+            ObjectData::native_object(data),
         );
-        Ok(object_instance.into())
+        Ok(instance)
     }
 }
 
@@ -171,17 +157,19 @@ pub struct ClassBuilder<'ctx, 'host> {
 impl<'ctx, 'host> ClassBuilder<'ctx, 'host> {
     pub(crate) fn new<T>(context: &'ctx mut Context<'host>) -> Self
     where
-        T: ClassConstructor,
+        T: Class,
     {
-        let mut builder =
-            ConstructorBuilder::new(context, NativeFunction::from_fn_ptr(T::raw_constructor));
+        let mut builder = ConstructorBuilder::new(
+            context,
+            NativeFunction::from_fn_ptr(|t, a, c| T::construct(t, a, c).map(JsValue::from)),
+        );
         builder.name(T::NAME);
         builder.length(T::LENGTH);
         Self { builder }
     }
 
-    pub(crate) fn build(self) -> JsFunction {
-        JsFunction::from_object_unchecked(self.builder.build().into())
+    pub(crate) fn build(self) -> StandardConstructor {
+        self.builder.build()
     }
 
     /// Add a method to the class.
@@ -189,10 +177,9 @@ impl<'ctx, 'host> ClassBuilder<'ctx, 'host> {
     /// It is added to `prototype`.
     pub fn method<N>(&mut self, name: N, length: usize, function: NativeFunction) -> &mut Self
     where
-        N: AsRef<str>,
+        N: Into<FunctionBinding>,
     {
-        self.builder
-            .method(function, js_string!(name.as_ref()), length);
+        self.builder.method(function, name, length);
         self
     }
 
@@ -206,10 +193,9 @@ impl<'ctx, 'host> ClassBuilder<'ctx, 'host> {
         function: NativeFunction,
     ) -> &mut Self
     where
-        N: AsRef<str>,
+        N: Into<FunctionBinding>,
     {
-        self.builder
-            .static_method(function, js_string!(name.as_ref()), length);
+        self.builder.static_method(function, name, length);
         self
     }
 

boa_engine/src/context/intrinsics.rs

@@ -58,8 +58,8 @@ impl Intrinsics {
     }
 }
 
-/// Store a builtin constructor (such as `Object`) and its corresponding prototype.
-#[derive(Debug, Trace, Finalize)]
+/// Stores a constructor (such as `Object`) and its corresponding prototype.
+#[derive(Debug, Trace, Finalize, Clone)]
 pub struct StandardConstructor {
     constructor: JsFunction,
     prototype: JsObject,
@@ -75,6 +75,14 @@ impl Default for StandardConstructor {
 }
 
 impl StandardConstructor {
+    /// Creates a new `StandardConstructor` from the constructor and the prototype.
+    pub(crate) fn new(constructor: JsFunction, prototype: JsObject) -> Self {
+        Self {
+            constructor,
+            prototype,
+        }
+    }
+
     /// Build a constructor with a defined prototype.
     fn with_prototype(prototype: JsObject) -> Self {
         Self {
@@ -85,7 +93,7 @@ impl StandardConstructor {
 
     /// Return the prototype of the constructor object.
     ///
-    /// This is the same as `Object.prototype`, `Array.prototype`, etc
+    /// This is the same as `Object.prototype`, `Array.prototype`, etc.
     #[inline]
     #[must_use]
     pub fn prototype(&self) -> JsObject {

boa_engine/src/context/mod.rs

@@ -29,7 +29,7 @@ use crate::{
     realm::Realm,
     script::Script,
     vm::{ActiveRunnable, CallFrame, Vm},
-    JsResult, JsString, JsValue, Source,
+    JsNativeError, JsResult, JsString, JsValue, Source,
 };
 use boa_ast::{expression::Identifier, StatementList};
 use boa_interner::Interner;
@@ -37,6 +37,8 @@ use boa_profiler::Profiler;
 
 use crate::vm::RuntimeLimits;
 
+use self::intrinsics::StandardConstructor;
+
 /// ECMAScript context. It is the primary way to interact with the runtime.
 ///
 /// `Context`s constructed in a thread share the same runtime, therefore it
@@ -317,9 +319,9 @@ impl<'host> Context<'host> {
         Ok(())
     }
 
-    /// Register a global class of type `T`, where `T` implements `Class`.
+    /// Registers a global class `C` in the currently active realm.
     ///
-    /// It will return an error if the global property is already defined.
+    /// Errors if the class has already been registered.
     ///
     /// # Example
     /// ```ignore
@@ -330,28 +332,74 @@ impl<'host> Context<'host> {
     ///    // ...
     /// }
     ///
-    /// context.register_global_class::<MyClass>();
+    /// context.register_global_class::<MyClass>()?;
     /// ```
-    pub fn register_global_class<T>(&mut self) -> JsResult<()>
-    where
-        T: Class,
-    {
-        let mut class_builder = ClassBuilder::new::<T>(self);
-        T::init(&mut class_builder)?;
+    pub fn register_global_class<C: Class>(&mut self) -> JsResult<()> {
+        if self.realm.has_class::<C>() {
+            return Err(JsNativeError::typ()
+                .with_message("cannot register a class twice")
+                .into());
+        }
+
+        let mut class_builder = ClassBuilder::new::<C>(self);
+        C::init(&mut class_builder)?;
 
         let class = class_builder.build();
         let property = PropertyDescriptor::builder()
-            .value(class)
-            .writable(T::ATTRIBUTES.writable())
-            .enumerable(T::ATTRIBUTES.enumerable())
-            .configurable(T::ATTRIBUTES.configurable());
+            .value(class.constructor())
+            .writable(C::ATTRIBUTES.writable())
+            .enumerable(C::ATTRIBUTES.enumerable())
+            .configurable(C::ATTRIBUTES.configurable());
 
         self.global_object()
-            .define_property_or_throw(js_string!(T::NAME), property, self)?;
+            .define_property_or_throw(js_string!(C::NAME), property, self)?;
+        self.realm.register_class::<C>(class);
 
         Ok(())
     }
 
+    /// Removes the global class `C` from the currently active realm, returning the constructor
+    /// and prototype of the class if `C` was registered.
+    ///
+    /// # Note
+    ///
+    /// This makes the constructor return an error on further calls, but note that this won't protect
+    /// static properties from being accessed within variables that stored the constructor before being
+    /// unregistered.  If you need that functionality, you can use a static accessor that first checks
+    /// if the class is registered ([`Context::has_global_class`]) before returning the static value.
+    ///
+    /// # Example
+    /// ```ignore
+    /// #[derive(Debug, Trace, Finalize)]
+    /// struct MyClass;
+    ///
+    /// impl Class for MyClass {
+    ///    // ...
+    /// }
+    ///
+    /// context.register_global_class::<MyClass>()?;
+    /// // ... code
+    /// context.unregister_global_class::<MyClass>()?;
+    /// ```
+    pub fn unregister_global_class<C: Class>(&mut self) -> JsResult<Option<StandardConstructor>> {
+        self.global_object()
+            .delete_property_or_throw(js_string!(C::NAME), self)?;
+        Ok(self.realm.unregister_class::<C>())
+    }
+
+    /// Checks if the currently active realm has the global class `C` registered.
+    #[must_use]
+    pub fn has_global_class<C: Class>(&self) -> bool {
+        self.realm.has_class::<C>()
+    }
+
+    /// Gets the constructor and prototype of the global class `C` if the currently active realm has
+    /// that class registered.
+    #[must_use]
+    pub fn get_global_class<C: Class>(&self) -> Option<StandardConstructor> {
+        self.realm.get_class::<C>()
+    }
+
     /// Gets the string interner.
     #[inline]
     #[must_use]

boa_engine/src/host_defined.rs

@@ -73,20 +73,12 @@ impl HostDefined {
     /// Panics if [`HostDefined`] field is borrowed.
     #[track_caller]
     pub fn get<T: NativeObject>(&self) -> Option<GcRef<'_, T>> {
-        let state = self.state.borrow();
-
-        state
-            .get(&TypeId::of::<T>())
-            .map(Box::as_ref)
-            .and_then(<dyn NativeObject>::downcast_ref::<T>)?;
-
-        Some(GcRef::map(state, |state| {
+        GcRef::try_map(self.state.borrow(), |state| {
             state
                 .get(&TypeId::of::<T>())
                 .map(Box::as_ref)
                 .and_then(<dyn NativeObject>::downcast_ref::<T>)
-                .expect("Should not fail")
-        }))
+        })
     }
 
     /// Get type T from [`HostDefined`], if it exits.
@@ -96,23 +88,15 @@ impl HostDefined {
     /// Panics if [`HostDefined`] field is borrowed.
     #[track_caller]
     pub fn get_mut<T: NativeObject>(&self) -> Option<GcRefMut<'_, HostDefinedMap, T>> {
-        let mut state = self.state.borrow_mut();
-
-        state
-            .get_mut(&TypeId::of::<T>())
-            .map(Box::as_mut)
-            .and_then(<dyn NativeObject>::downcast_mut::<T>)?;
-
-        Some(GcRefMut::map(
-            state,
+        GcRefMut::try_map(
+            self.state.borrow_mut(),
             |state: &mut FxHashMap<TypeId, Box<dyn NativeObject>>| {
                 state
                     .get_mut(&TypeId::of::<T>())
                     .map(Box::as_mut)
                     .and_then(<dyn NativeObject>::downcast_mut::<T>)
-                    .expect("Should not fail")
             },
-        ))
+        )
     }
 
     /// Clears all the objects.

boa_engine/src/object/mod.rs

@@ -56,6 +56,7 @@ use crate::{
         typed_array::{integer_indexed_object::IntegerIndexed, TypedArrayKind},
         DataView, Date, Promise, RegExp,
     },
+    context::intrinsics::StandardConstructor,
     js_string,
     module::ModuleNamespace,
     native_function::NativeFunction,
@@ -2004,8 +2005,8 @@ impl Object {
 ///
 /// There are two implementations:
 ///  - From a single type `T` which implements `Into<FunctionBinding>` which sets the binding
-/// name and the function name to the same value
-///  - From a tuple `(B: Into<PropertyKey>, N: AsRef<str>)` the `B` is the binding name
+/// name and the function name to the same value.
+///  - From a tuple `(B: Into<PropertyKey>, N: Into<JsString>)`, where the `B` is the binding name
 /// and the `N` is the function name.
 #[derive(Debug, Clone)]
 pub struct FunctionBinding {
@@ -2023,6 +2024,16 @@ impl From<JsString> for FunctionBinding {
     }
 }
 
+impl From<JsSymbol> for FunctionBinding {
+    #[inline]
+    fn from(binding: JsSymbol) -> Self {
+        Self {
+            name: binding.fn_name(),
+            binding: binding.into(),
+        }
+    }
+}
+
 impl<B, N> From<(B, N)> for FunctionBinding
 where
     B: Into<PropertyKey>,
@@ -2510,7 +2521,7 @@ impl<'ctx, 'host> ConstructorBuilder<'ctx, 'host> {
 
     /// Build the constructor function object.
     #[must_use]
-    pub fn build(mut self) -> JsFunction {
+    pub fn build(mut self) -> StandardConstructor {
         // Create the native function
         let function = Function::new(
             FunctionKind::Native {
@@ -2593,6 +2604,6 @@ impl<'ctx, 'host> ConstructorBuilder<'ctx, 'host> {
             );
         }
 
-        JsFunction::from_object_unchecked(constructor)
+        StandardConstructor::new(JsFunction::from_object_unchecked(constructor), prototype)
     }
 }

boa_engine/src/realm.rs

@@ -6,8 +6,16 @@
 //!
 //! A realm is represented in this implementation as a Realm struct with the fields specified from the spec.
 
+use std::any::TypeId;
+
+use rustc_hash::FxHashMap;
+
 use crate::{
-    context::{intrinsics::Intrinsics, HostHooks},
+    class::Class,
+    context::{
+        intrinsics::{Intrinsics, StandardConstructor},
+        HostHooks,
+    },
     environments::DeclarativeEnvironment,
     module::Module,
     object::shape::RootShape,
@@ -15,7 +23,6 @@ use crate::{
 };
 use boa_gc::{Finalize, Gc, GcRefCell, Trace};
 use boa_profiler::Profiler;
-use rustc_hash::FxHashMap;
 
 /// Representation of a Realm.
 ///
@@ -52,6 +59,7 @@ struct Inner {
     global_this: JsObject,
     template_map: GcRefCell<FxHashMap<u64, JsObject>>,
     loaded_modules: GcRefCell<FxHashMap<JsString, Module>>,
+    host_classes: GcRefCell<FxHashMap<TypeId, StandardConstructor>>,
 
     host_defined: HostDefined,
 }
@@ -77,6 +85,7 @@ impl Realm {
                 global_this,
                 template_map: GcRefCell::default(),
                 loaded_modules: GcRefCell::default(),
+                host_classes: GcRefCell::default(),
                 host_defined: HostDefined::default(),
             }),
         };
@@ -102,6 +111,25 @@ impl Realm {
         &self.inner.host_defined
     }
 
+    /// Checks if this `Realm` has the class `C` registered into its class map.
+    #[must_use]
+    pub fn has_class<C: Class>(&self) -> bool {
+        self.inner
+            .host_classes
+            .borrow()
+            .contains_key(&TypeId::of::<C>())
+    }
+
+    /// Gets the constructor and prototype of the class `C` if it is registered in the class map.
+    #[must_use]
+    pub fn get_class<C: Class>(&self) -> Option<StandardConstructor> {
+        self.inner
+            .host_classes
+            .borrow()
+            .get(&TypeId::of::<C>())
+            .cloned()
+    }
+
     pub(crate) fn environment(&self) -> &Gc<DeclarativeEnvironment> {
         &self.inner.environment
     }
@@ -142,6 +170,20 @@ impl Realm {
         self.inner.template_map.borrow().get(&site).cloned()
     }
 
+    pub(crate) fn register_class<C: Class>(&self, spec: StandardConstructor) {
+        self.inner
+            .host_classes
+            .borrow_mut()
+            .insert(TypeId::of::<C>(), spec);
+    }
+
+    pub(crate) fn unregister_class<C: Class>(&self) -> Option<StandardConstructor> {
+        self.inner
+            .host_classes
+            .borrow_mut()
+            .remove(&TypeId::of::<C>())
+    }
+
     pub(crate) fn addr(&self) -> *const () {
         let ptr: *const _ = &*self.inner;
         ptr.cast()

boa_engine/src/string/common.rs

@@ -94,6 +94,19 @@ impl StaticJsStrings {
         (SYMBOL_TO_PRIMITIVE, "Symbol.toPrimitive"),
         (SYMBOL_TO_STRING_TAG, "Symbol.toStringTag"),
         (SYMBOL_UNSCOPABLES, "Symbol.unscopables"),
+        (FN_SYMBOL_ASYNC_ITERATOR, "[Symbol.asyncIterator]"),
+        (FN_SYMBOL_HAS_INSTANCE, "[Symbol.hasInstance]"),
+        (FN_SYMBOL_IS_CONCAT_SPREADABLE, "[Symbol.isConcatSpreadable]"),
+        (FN_SYMBOL_ITERATOR, "[Symbol.iterator]"),
+        (FN_SYMBOL_MATCH, "[Symbol.match]"),
+        (FN_SYMBOL_MATCH_ALL, "[Symbol.matchAll]"),
+        (FN_SYMBOL_REPLACE, "[Symbol.replace]"),
+        (FN_SYMBOL_SEARCH, "[Symbol.search]"),
+        (FN_SYMBOL_SPECIES, "[Symbol.species]"),
+        (FN_SYMBOL_SPLIT, "[Symbol.split]"),
+        (FN_SYMBOL_TO_PRIMITIVE, "[Symbol.toPrimitive]"),
+        (FN_SYMBOL_TO_STRING_TAG, "[Symbol.toStringTag]"),
+        (FN_SYMBOL_UNSCOPABLES, "[Symbol.unscopables]"),
         // Builtins
         (ARRAY, "Array"),
         (ARRAY_BUFFER, "ArrayBuffer"),

boa_engine/src/symbol.rs

@@ -96,6 +96,24 @@ impl WellKnown {
         }
     }
 
+    const fn fn_name(self) -> JsString {
+        match self {
+            Self::AsyncIterator => StaticJsStrings::FN_SYMBOL_ASYNC_ITERATOR,
+            Self::HasInstance => StaticJsStrings::FN_SYMBOL_HAS_INSTANCE,
+            Self::IsConcatSpreadable => StaticJsStrings::FN_SYMBOL_IS_CONCAT_SPREADABLE,
+            Self::Iterator => StaticJsStrings::FN_SYMBOL_ITERATOR,
+            Self::Match => StaticJsStrings::FN_SYMBOL_MATCH,
+            Self::MatchAll => StaticJsStrings::FN_SYMBOL_MATCH_ALL,
+            Self::Replace => StaticJsStrings::FN_SYMBOL_REPLACE,
+            Self::Search => StaticJsStrings::FN_SYMBOL_SEARCH,
+            Self::Species => StaticJsStrings::FN_SYMBOL_SPECIES,
+            Self::Split => StaticJsStrings::FN_SYMBOL_SPLIT,
+            Self::ToPrimitive => StaticJsStrings::FN_SYMBOL_TO_PRIMITIVE,
+            Self::ToStringTag => StaticJsStrings::FN_SYMBOL_TO_STRING_TAG,
+            Self::Unscopables => StaticJsStrings::FN_SYMBOL_UNSCOPABLES,
+        }
+    }
+
     const fn hash(self) -> u64 {
         self as u64
     }
@@ -163,7 +181,7 @@ impl JsSymbol {
         })
     }
 
-    /// Returns the `Symbol`s description.
+    /// Returns the `Symbol` description.
     #[inline]
     #[must_use]
     pub fn description(&self) -> Option<JsString> {
@@ -182,6 +200,24 @@ impl JsSymbol {
         }
     }
 
+    /// Returns the `Symbol` as a function name.
+    ///
+    /// Equivalent to `[description]`, but returns the empty string if the symbol doesn't have a
+    /// description.
+    #[inline]
+    #[must_use]
+    pub fn fn_name(&self) -> JsString {
+        if let UnwrappedTagged::Tag(tag) = self.repr.unwrap() {
+            // SAFETY: All tagged reprs always come from `WellKnown` itself, making
+            // this operation always safe.
+            let wk = unsafe { WellKnown::from_tag(tag).unwrap_unchecked() };
+            return wk.fn_name();
+        }
+        self.description()
+            .map(|s| js_string!(utf16!("["), &*s, utf16!("]")))
+            .unwrap_or_default()
+    }
+
     /// Returns the `Symbol`s hash.
     ///
     /// The hash is guaranteed to be unique.

boa_examples/src/bin/classes.rs

@@ -64,18 +64,19 @@ impl Class for Person {
     // NOTE: The default value of `LENGTH` is `0`.
     const LENGTH: usize = 2;
 
-    // This is what is called when we construct a `Person` with the expression `new Person()`.
-    fn constructor(_this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self> {
+    // This is what is internally called when we construct a `Person` with the expression `new Person()`.
+    fn make_data(_this: &JsValue, args: &[JsValue], context: &mut Context<'_>) -> JsResult<Self> {
         // We get the first argument. If it is unavailable we default to `undefined`,
         // and then we call `to_string()`.
         //
         // This is equivalent to `String(arg)`.
         let name = args.get_or_undefined(0).to_string(context)?;
+
         // We get the second argument. If it is unavailable we default to `undefined`,
         // and then we call `to_u32`.
         //
         // This is equivalent to `arg | 0`.
-        let age = args.get(1).cloned().unwrap_or_default().to_u32(context)?;
+        let age = args.get_or_undefined(1).to_u32(context)?;
 
         // We construct a new native struct `Person`
         let person = Person { name, age };
@@ -88,14 +89,18 @@ impl Class for Person {
         // We add a inheritable method `sayHello` with `0` arguments of length.
         //
         // This function is added to the `Person` prototype.
-        class.method("sayHello", 0, NativeFunction::from_fn_ptr(Self::say_hello));
+        class.method(
+            js_string!("sayHello"),
+            0,
+            NativeFunction::from_fn_ptr(Self::say_hello),
+        );
         // We add a static method `is` using a closure, but it must be convertible
-        // to a NativeFunction.
-        // This means it must not contain state, or the code won't compile.
+        // to a `NativeFunction`. The `NativeFunction` API has more information on which type of
+        // Rust functions can be used to create `NativeFunction`s.
         //
         // This function is added to the `Person` class.
         class.static_method(
-            "is",
+            js_string!("is"),
             1,
             NativeFunction::from_fn_ptr(|_this, args, _ctx| {
                 if let Some(arg) = args.get(0) {

boa_gc/src/cell.rs

@@ -269,6 +269,31 @@ impl<'a, T: ?Sized> GcRef<'a, T> {
         }
     }
 
+    /// Tries to make a new `GcCellRef` from a component of the borrowed data, returning `None`
+    /// if the mapping function returns `None`.
+    ///
+    /// The `GcCell` is already immutably borrowed, so this cannot fail.
+    ///
+    /// This is an associated function that needs to be used as `GcCellRef::try_map(...)`.
+    /// A method would interfere with methods of the same name on the contents
+    /// of a `GcCellRef` used through `Deref`.
+    pub fn try_map<U, F>(orig: Self, f: F) -> Option<GcRef<'a, U>>
+    where
+        U: ?Sized,
+        F: FnOnce(&T) -> Option<&U>,
+    {
+        let ret = GcRef {
+            flags: orig.flags,
+            value: f(orig.value)?,
+        };
+
+        // We have to tell the compiler not to call the destructor of GcCellRef,
+        // because it will update the borrow flags.
+        std::mem::forget(orig);
+
+        Some(ret)
+    }
+
     /// Makes a new `GcCellRef` from a component of the borrowed data.
     ///
     /// The `GcCell` is already immutably borrowed, so this cannot fail.
@@ -362,6 +387,35 @@ pub struct GcRefMut<'a, T: ?Sized + 'static, U: ?Sized = T> {
 }
 
 impl<'a, T: ?Sized, U: ?Sized> GcRefMut<'a, T, U> {
+    /// Tries to make a new `GcCellRefMut` for a component of the borrowed data, returning `None`
+    /// if the mapping function returns `None`.
+    ///
+    /// The `GcCellRefMut` is already mutably borrowed, so this cannot fail.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `GcCellRefMut::map(...)`. A method would interfere with methods of the same
+    /// name on the contents of a `GcCell` used through `Deref`.
+    pub fn try_map<V, F>(orig: Self, f: F) -> Option<GcRefMut<'a, T, V>>
+    where
+        V: ?Sized,
+        F: FnOnce(&mut U) -> Option<&mut V>,
+    {
+        #[allow(trivial_casts)]
+        // SAFETY: This is safe as `GcCellRefMut` is already borrowed, so the value is rooted.
+        let value = unsafe { &mut *(orig.value as *mut U) };
+
+        let ret = GcRefMut {
+            gc_cell: orig.gc_cell,
+            value: f(value)?,
+        };
+
+        // We have to tell the compiler not to call the destructor of GcCellRef,
+        // because it will update the borrow flags.
+        std::mem::forget(orig);
+
+        Some(ret)
+    }
+
     /// Makes a new `GcCellRefMut` for a component of the borrowed data, e.g., an enum
     /// variant.
     ///