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User Guide #11 - Ruby - methods

methods, Ruby, ruby lesson, ruby уроки, user guide, методы, руководство пользователя

What is a method? In OO programming, we don't think of operating on data directly from outside an object; rather, objects have some understanding of how to operate on themselves (when asked nicely to do so). You might say we pass messages to an object, and those messages will generally elicit some kind of an action or meaningful reply. This ought to happen without our necessarily knowing or caring how the object really works inside. The tasks we are allowed to ask an object to perform (or equivalently, the messages it understands) are that object's methods .

In ruby, we invoke a method of an object with dot notation (just as in C++ or Java). The object being talked to is named to the left of the dot.

ruby> "abcdef".length
   6

Intuitively, this string object is being asked how long it is . Technically, we are invoking the length method of the object "abcdef".

Other objects may have a slightly different interpretation of length , or none at all. Decisions about how to respond to a message are made on the fly, during program execution, and the action taken may change depending on what a variable refers to.

ruby> foo = "abc"
   "abc"
ruby> foo.length
   3
ruby> foo = ["abcde", "fghij"]
   ["abcde", "fghij"]
ruby> foo.length
   2

What we mean by length can vary depending on what object we are talking about. The first time we ask foo for its length in the above example, it refers to a simple string, and there can only be one sensible answer. The second time, foo refers to an array, and we might reasonably think of its length as either 2, 5, or 10; but the most generally applicable answer is of course 2 (the other kinds of length can be figured out if wished).

ruby> foo[0].length
   5
ruby> foo[0].length + foo[1].length
   10

The thing to notice here is that an array knows something about what it means to be an array . Pieces of data in ruby carry such knowledge with them, so that the demands made on them can automatically be satisfied in the various appropriate ways. This relieves the programmer from the burden of memorizing a great many specific function names, because a relatively small number of method names, corresponding to concepts that we know how to express in natural language, can be applied to different kinds of data and the results will be what we expect. This feature of OO programming languages is called polymorphism .

When an object receives a message that it does not understand, an error is "raised":

ruby> foo = 5
   5
ruby> foo.length
ERR: (eval):1: undefined method `length' for 5(Fixnum)

So it is necessary to know what methods are acceptable to an object, though we need not know how the methods are processed.

If arguments are given to a method, they are generally surrounded by parentheses,

object.method(arg1, arg2)

but they can be omitted if doing so does not cause ambiguity.

object.method arg1, arg2

There is a special variable self in ruby; it refers to whatever object calls a method. This happens so often that for convenience the " self." may be omitted from method calls from an object to itself:

self.method_name(args...)

is the same as

method_name(args...)

What we would think of traditionally as a function call is just this abbreviated way of writing method invocations by self. This makes ruby what is called a pure object oriented language. Still, functional methods behave quite similarly to the functions in other programming languages for the benefit of those who do not grok how function calls are really object methods in ruby. We can speak of functions as if they were not really object methods if we want to.

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МБ
April 21, 2019, 9:40 a.m.
Моисей Бушуев

Qt - Test 001. Signals and slots

  • Result:0points,
  • Rating points-10
AA
April 17, 2019, 7:40 p.m.
Anton Ablin

Qt - Test 001. Signals and slots

  • Result:73points,
  • Rating points1
E
April 17, 2019, 6:16 p.m.
Evgeny

Qt - Test 001. Signals and slots

  • Result:100points,
  • Rating points10
Last comments
April 21, 2019, 4:22 p.m.
Евгений Легоцкой

Через метод setIcon table.horizontalHeaderItem(0).setIcon("qrc://path/to/icon.png")
April 21, 2019, 3:48 p.m.
Евгений Легоцкой

Добрый день! Спасибо за комментарий. Там действительно лучше будет сделать с инициализацией по умолчанию.
U
April 18, 2019, 3:37 p.m.
Unreal_man

А как иконку в хедер задать?
u
April 18, 2019, 2:15 a.m.
uaa

доброго времени,большое спасибо за пример для начинающего)при адаптации к своему проекту столкнулся с таким ньансом:в vepolyline.h в 47 строке нужна инициализация по умолчанию: int m_pointF...
E
April 11, 2019, 12:49 p.m.
Evgeny

Спасибо за ответ) У меня компоновщик на нее ругался просто. Оказалось, просто забыл Q_OBJECT в начале класса указать.
Now discuss on the forum
April 21, 2019, 4:16 p.m.
Евгений Легоцкой

Приветствую Нужно сохранять где-то выбранное значение, а потом восстанавливать его. Или использовать QSettings или добавить метод open(), в который передавать начальные значения для того...
R
April 19, 2019, 9:55 a.m.
RED_Spider

мені важко це зараз навіть перевірити, тому що знайшов коміт, це ще було в 2016 році, і цей код не буде працювати коректно зараз, єдине скажу що це були QThread
i
April 17, 2019, 3:03 p.m.
ilya.guzikov

BlinCT, на стороне ++ это делать необходимо так как в qml при использовании функции append происходит перерисовка всех точек лини(как я понимаю) и из-за этого при использовании больших массиво...
April 10, 2019, 11:20 a.m.
Алексей Внуков

может тоже кому надо будет - QML не принимает QVector<QVector<int>> , при попытке вывести полученый вектор QML показывает что это QVariant(QVector<QVector<int> ...
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