Now, assume one also desires the ability to add borders to windows. Again, the original Window class has no support. The ScrollingWindow subclass now poses a problem, because it has effectively created a new kind of window. If one wishes to add border support to many but not all windows, one must create subclasses WindowWithBorder and ScrollingWindowWithBorder etc. This problem gets worse with every new feature or window subtype to be added. For the decorator solution, we simply create a new BorderedWindowDecorator—at runtime, we can decorate existing windows with the ScrollingWindowDecorator or the BorderedWindowDecorator or both, as we see fit. Notice that if the functionality needs to be added to all Windows, you could modify the base class and that will do. On the other hand, sometimes (e.g., using external frameworks) it is not possible, legal, or convenient to modify the base class.
The delegate injection point must be an injected field, initializer method parameter or bean constructor method parameter. If an injection point that is not an injected field, initializer method parameter or bean constructor method parameter is annotated @Delegate, the container automatically detects the problem and treats it as a definition error.
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... the keyword starting the line that heads a block draws a lot of attention to it. This is true for "if", "while", "for", "try", "def" and "class". But the "using" keyword (or any other keyword in its place) doesn't deserve that attention; the emphasis should be on the decorator or decorators inside the suite, since those are the important modifiers to the function definition that follows. ...
Two decorators (classmethod() and staticmethod()) have been available in Python since version 2.2. It's been assumed since approximately that time that some syntactic support for them would eventually be added to the language. Given this assumption, one might wonder why it's been so difficult to arrive at a consensus. Discussions have raged off-and-on at times in both comp.lang.python and the python-dev mailing list about how best to implement function decorators. There is no one clear reason why this should be so, but a few problems seem to be most divisive.
The decorator pattern is a design pattern that allows you to wrap an object such that it will appear to execute a given behavior in many different ways at different points in program execution. This is especially useful when you want an object to have different behaviors at but are unable to mutate the object. The decorator pattern is a useful way to implement dynamic behavior without needing an extended inheritance-based class hierarchy. To use the decorator pattern you need four elements: a component interface; a concrete component; a decorator abstraction; and, a concrete decorator. The interface sets the contract for both component and decorator behavior, the decorator abstraction contains a pointer to some concrete component, and the concrete decorators wrap a concrete component and override behavior if desired.
When we instantiate a SimpleMessage and then pass it to the various decorators, we now get new behavior. Moreover, since both the concrete component and the concrete decorators all implement / descend from IMessage, they are interchangeable as far as the program is concerned, meaning that we can loop over them together. Further, rather than having to create a new ExcitedAndQuizzicalMessageDecorator class, we were able to achieve the same effect by double wrapping a SimpleMessage object (first in an ExcitedMessageDecorator and then in a QuizzicalMessageDecorator). Finally, note that despite having been passed into various decorators, our simpleMsg object remains unchanged at the end of the program.
The decorator pattern can be used to extend (decorate) the functionality of a certain object statically, or in some cases at run-time, independently of other instances of the same class, provided some groundwork is done at design time. This is achieved by designing a new Decorator class that wraps the original class. This wrapping could be achieved by the following sequence of steps:
Speed, portability and permanence also make aerosol paint a common graffiti medium. In the late 1970s, street graffiti writers' signatures and murals became more elaborate and a unique style developed as a factor of the aerosol medium and the speed required for illicit work. Many now recognize graffiti and street art as a unique art form and specifically manufactured aerosol paints are made for the graffiti artist. A stencil protects a surface, except the specific shape to be painted. Stencils can be purchased as movable letters, ordered as professionally cut logos or hand-cut by artists.
The term outsider art was coined by art critic Roger Cardinal in 1972 as an English synonym for art brut (French: [aʁ bʁyt], "raw art" or "rough art"), a label created by French artist Jean Dubuffet to describe art created outside the boundaries of official culture; Dubuffet focused particularly on art by insane-asylum inmates. Outsider art has emerged as a successful art marketing category (an annual Outsider Art Fair has taken place in New York since 1992). The term is sometimes misapplied as a catch-all marketing label for art created by people outside the mainstream "art world," regardless of their circumstances or the content of their work.
Concrete Decorator: Here we have two concrete decorators, ExcitedMessageDecorator and QuizzicalMessageDecorator, each of which descends from the abstract MessageDecorator class. However, these decorators do have special behavior in that they override the GetMessage and PrintMessage behaviors and enhance them by calling the base version from MessageDecorator (which in turn delegates to the relevant IMessage object) and then appending exclamations.
Using functions with "action-at-a-distance" through sys.settraceback may be okay for an obscure feature that can't be had any other way yet doesn't merit changes to the language, but that's not the situation for decorators. The widely held view here is that decorators need to be added as a syntactic feature to avoid the problems with the postfix notation used in 2.2 and 2.3. Decorators are slated to be an important new language feature and their design needs to be forward-looking, not constrained by what can be implemented in 2.3.
In Spanish art, a bodegón is a still life painting depicting pantry items, such as victuals, game, and drink, often arranged on a simple stone slab, and also a painting with one or more figures, but significant still life elements, typically set in a kitchen or tavern. Starting in the Baroque period, such paintings became popular in Spain in the second quarter of the 17th century. The tradition of still life painting appears to have started and was far more popular in the contemporary Low Countries, today Belgium and Netherlands (then Flemish and Dutch artists), than it ever was in southern Europe. Northern still lifes had many subgenres: the breakfast piece was augmented by the trompe-l'œil, the flower bouquet, and the vanitas. In Spain there were much fewer patrons for this sort of thing, but a type of breakfast piece did become popular, featuring a few objects of food and tableware laid on a table.