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LibJS: Implement Iterator.prototype.filter
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3 changed files with 224 additions and 0 deletions
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@ -31,6 +31,7 @@ ThrowCompletionOr<void> IteratorPrototype::initialize(Realm& realm)
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u8 attr = Attribute::Writable | Attribute::Configurable;
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define_native_function(realm, vm.well_known_symbol_iterator(), symbol_iterator, 0, attr);
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define_native_function(realm, vm.names.map, map, 1, attr);
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define_native_function(realm, vm.names.filter, filter, 1, attr);
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return {};
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}
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@ -103,4 +104,70 @@ JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::map)
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return result;
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}
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// 3.1.3.3 Iterator.prototype.filter ( predicate ), https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.filter
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JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::filter)
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{
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auto& realm = *vm.current_realm();
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auto predicate = vm.argument(0);
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// 1. Let O be the this value.
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// 2. If O is not an Object, throw a TypeError exception.
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auto object = TRY(this_object(vm));
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// 3. If IsCallable(predicate) is false, throw a TypeError exception.
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if (!predicate.is_function())
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return vm.throw_completion<TypeError>(ErrorType::NotAFunction, "predicate"sv);
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// 4. Let iterated be ? GetIteratorDirect(O).
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auto iterated = TRY(get_iterator_direct(vm, object));
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// 5. Let closure be a new Abstract Closure with no parameters that captures iterated and predicate and performs the following steps when called:
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IteratorHelper::Closure closure = [predicate = NonnullGCPtr { predicate.as_function() }](auto& iterator) -> ThrowCompletionOr<Value> {
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auto& vm = iterator.vm();
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auto const& iterated = iterator.underlying_iterator();
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// a. Let counter be 0.
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// b. Repeat,
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while (true) {
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// i. Let next be ? IteratorStep(iterated).
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auto next = TRY(iterator_step(vm, iterated));
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// ii. If next is false, return undefined.
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if (!next)
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return iterator.result(js_undefined());
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// iii. Let value be ? IteratorValue(next).
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auto value = TRY(iterator_value(vm, *next));
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// iv. Let selected be Completion(Call(predicate, undefined, « value, 𝔽(counter) »)).
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auto selected = call(vm, *predicate, js_undefined(), value, Value { iterator.counter() });
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// v. IfAbruptCloseIterator(selected, iterated).
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if (selected.is_error())
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return iterator.close_result(selected.release_error());
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// vii. Set counter to counter + 1.
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// NOTE: We do this step early to ensure it occurs before returning.
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iterator.increment_counter();
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// vi. If ToBoolean(selected) is true, then
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if (selected.value().to_boolean()) {
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// 1. Let completion be Completion(Yield(value)).
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// 2. IfAbruptCloseIterator(completion, iterated).
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return iterator.result(value);
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}
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}
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};
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// 6. Let result be CreateIteratorFromClosure(closure, "Iterator Helper", %IteratorHelperPrototype%, « [[UnderlyingIterator]] »).
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// 7. Set result.[[UnderlyingIterator]] to iterated.
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auto result = TRY(IteratorHelper::create(realm, move(iterated), move(closure)));
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// 8. Return result.
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return result;
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}
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}
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@ -23,6 +23,7 @@ private:
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JS_DECLARE_NATIVE_FUNCTION(symbol_iterator);
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JS_DECLARE_NATIVE_FUNCTION(map);
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JS_DECLARE_NATIVE_FUNCTION(filter);
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};
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}
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