what is this new “in” keyword in swift 3

Tags: swift swift3
By : Bob5421
Source: Stackoverflow.com

I have just opened a swift 2 project with last Xcode version. Xcode suggest me to auto convert my code to swift 3.

Here is something strange:

func numberOfSections(in tableView: UITableView) -> Int
    return 1

func tableView(_ tableView: MyTableView,  numberOfRowsInSection section: Int) -> Int
    return 10

If you look, Xcode added a "in" keyword for the numberOfSections method. But he did nothing for the numberOfRowsInSection method. I do not understand why.

What is this "in" keyword in Swift 3 ?

By : Bob5421


It's not a keyword. It's the name of the first parameter in the method.

In Swift2 the method was...

func numberOfSections(inTableView: UITableView) -> Int

... and it would be called like...


In Swift 3 there is a lot of emphasis on making function names more verb based and removing redundant inferred or implied type from the method names. Also, the first parameter name of methods is now required.

All these changes lead to the name being updated to what you have seen and the call becomes...

numberOfSections(in: tableView)

You can read more about the changes in Swift 3 in Apple's API Guidelines.

I would suggest the following general design pattern. It wastes an additional pointer, but will enforce the requirement that the const object will be able to only access const methods of the private object:

class ObjectImpl;

class const_Object {


  const_Object(const ObjectImpl* object_impl)
    : _impl(object_impl);

  // Only const methods

  const ObjectImpl* _impl;

class Object : public const_Object
  Object(ObjectImpl* object_impl)
    : const_Object(object_impl), _impl(object_impl);

  // non-const methods go here.

  ObjectImpl* _impl;

Adding to Ian's answer, Any complex element that is named by root element will have factory method annotated with @XmlElementDecl().

You can resolve this, by moving the complex type declaration inline like below.

<xsd:schema xmlns= "http://www.foo.org/bar" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:annox="http://annox.dev.java.net" xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
    targetNamespace="http://www.foo.org/bar" jaxb:extensionBindingPrefixes="annox"
    jaxb:version="2.1" elementFormDefault="qualified">
    <xsd:element name="unit">
                <xsd:any processContents="skip" />

ObjectFactory.class (no JAXBElement factory method generated here)

public class ObjectFactory {

     * Create a new ObjectFactory that can be used to create new instances of schema derived classes for package: org.foo.bar
    public ObjectFactory() {

     * Create an instance of {@link Unit }
    public Unit createUnit() {
        return new Unit();


Test class:

public void testUnmarshalling() throws JAXBException, SAXException {
    JAXBContext context = JAXBContext.newInstance(Unit.class);

    Unmarshaller unmarshaller = context.createUnmarshaller();

            .newSchema(new StreamSource(getClass().getClassLoader().getResourceAsStream("common.xsd"))));

    Object unit = unmarshaller.unmarshal(getClass().getResourceAsStream("unit.xml"));

    System.out.println(">>> Class is: " + unit.getClass().getName());

    StringWriter writer = new StringWriter();
    context.createMarshaller().marshal(unit, writer);

    System.out.println(">>> XML is: " + writer.toString());

    //assertTrue(unit instanceof Unit);

Test xml:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<unit xmlns="http://www.foo.org/bar">

output :

>>> Class is: org.foo.bar.Unit
>>> XML is: <?xml version="1.0" encoding="UTF-8" standalone="yes"?><unit xmlns="http://www.foo.org/bar"><text>Name</text></unit>
By : ulab

This video can help you solving your question :)
By: admin