LibJS: Add a PropertyName class that represents a string or a number

Now that we have two separate storages for Object properties depending
on what kind of index they have, it's nice to have an abstraction that
still allows us to say "here's a property name".

We use PropertyName to always choose the optimal storage path directly
while interpreting the AST. :^)

Libraries/LibJS/AST.cpp

@@ -855,13 +855,17 @@ void MemberExpression::dump(int indent) const
     m_property->dump(indent + 1);
 }
 
-FlyString MemberExpression::computed_property_name(Interpreter& interpreter) const
+PropertyName MemberExpression::computed_property_name(Interpreter& interpreter) const
 {
     if (!is_computed()) {
         ASSERT(m_property->is_identifier());
-        return static_cast<const Identifier&>(*m_property).string();
+        return PropertyName(static_cast<const Identifier&>(*m_property).string());
     }
-    return m_property->execute(interpreter).to_string();
+    auto index = m_property->execute(interpreter);
+    // FIXME: What about non-integer numbers tho.
+    if (index.is_number())
+        return PropertyName(index.to_i32());
+    return PropertyName(index.to_string());
 }
 
 Value MemberExpression::execute(Interpreter& interpreter) const

Libraries/LibJS/AST.h

@@ -33,6 +33,7 @@
 #include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibJS/Forward.h>
+#include <LibJS/Runtime/PropertyName.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
@@ -672,7 +673,7 @@ public:
     const Expression& object() const { return *m_object; }
     const Expression& property() const { return *m_property; }
 
-    FlyString computed_property_name(Interpreter&) const;
+    PropertyName computed_property_name(Interpreter&) const;
 
 private:
     virtual bool is_member_expression() const override { return true; }

Libraries/LibJS/Runtime/Object.cpp

@@ -150,6 +150,13 @@ Optional<Value> Object::get(const FlyString& property_name) const
     return {};
 }
 
+Optional<Value> Object::get(PropertyName property_name) const
+{
+    if (property_name.is_number())
+        return get_by_index(property_name.as_number());
+    return get(property_name.as_string());
+}
+
 void Object::put_by_index(i32 property_index, Value value)
 {
     if (property_index < 0)
@@ -189,6 +196,13 @@ void Object::put(const FlyString& property_name, Value value)
     put_own_property(*this, property_name, value);
 }
 
+void Object::put(PropertyName property_name, Value value)
+{
+    if (property_name.is_number())
+        return put_by_index(property_name.as_number(), value);
+    return put(property_name.as_string(), value);
+}
+
 void Object::put_native_function(const FlyString& property_name, AK::Function<Value(Interpreter&)> native_function, i32 length)
 {
     auto* function = heap().allocate<NativeFunction>(move(native_function));

Libraries/LibJS/Runtime/Object.h

@@ -31,6 +31,7 @@
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/Cell.h>
 #include <LibJS/Runtime/PrimitiveString.h>
+#include <LibJS/Runtime/PropertyName.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
@@ -45,9 +46,11 @@ public:
 
     Optional<Value> get_by_index(i32 property_index) const;
     Optional<Value> get(const FlyString& property_name) const;
+    Optional<Value> get(PropertyName) const;
 
     void put_by_index(i32 property_index, Value);
     void put(const FlyString& property_name, Value);
+    void put(PropertyName, Value);
 
     virtual Optional<Value> get_own_property(const Object& this_object, const FlyString& property_name) const;
     virtual bool put_own_property(Object& this_object, const FlyString& property_name, Value);

Libraries/LibJS/Runtime/PropertyName.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/FlyString.h>
+
+namespace JS {
+
+class PropertyName {
+public:
+    enum class Type {
+        Number,
+        String,
+    };
+
+    explicit PropertyName(i32 index)
+        : m_type(Type::Number)
+        , m_number(index)
+    {
+        ASSERT(m_number >= 0);
+    }
+
+    explicit PropertyName(const FlyString& string)
+        : m_type(Type::String)
+        , m_string(string)
+    {
+    }
+
+    bool is_number() const { return m_type == Type::Number; }
+    bool is_string() const { return m_type == Type::String; }
+
+    i32 as_number() const { return m_number; }
+    const FlyString& as_string() const { return m_string; }
+
+private:
+    Type m_type;
+    FlyString m_string;
+    i32 m_number { 0 };
+};
+
+}