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 container must inject a delegate object to the delegate injection point. The delegate object implements the delegate type and delegates method invocations to remaining uninvoked decorators and eventually to the bean. When the container calls a decorator during business method interception, the decorator may invoke any method of the delegate object.


Note that greet_bob(say_hello) refers to two functions, but in different ways: greet_bob() and say_hello. The say_hello function is named without parentheses. This means that only a reference to the function is passed. The function is not executed. The greet_bob() function, on the other hand, is written with parentheses, so it will be called as usual.
Oil painting is the process of painting with pigments that are bound with a medium of drying oil, such as linseed oil, which was widely used in early modern Europe. Often the oil was boiled with a resin such as pine resin or even frankincense; these were called 'varnishes' and were prized for their body and gloss. Oil paint eventually became the principal medium used for creating artworks as its advantages became widely known. The transition began with Early Netherlandish painting in northern Europe, and by the height of the Renaissance oil painting techniques had almost completely replaced tempera paints in the majority of Europe.
This code works for our purposes but it’s not exactly dynamic. If we wanted our initial simpleMsg object to sometimes act excited and sometimes quizzical, we could only do so by instantiating entirely new objects from the relevant subclass. Moreover, the ExcitedAndQuizzicalMessage is really just a combination of ExcitedMessage and QuizzicalMessage and probably shouldn’t have its own class. To fix these problems, let’s now return to the decorator pattern and see how it might help us.
Allegory is a figurative mode of representation conveying meaning other than the literal. Allegory communicates its message by means of symbolic figures, actions or symbolic representation. Allegory is generally treated as a figure of rhetoric, but an allegory does not have to be expressed in language: it may be addressed to the eye, and is often found in realistic painting. An example of a simple visual allegory is the image of the grim reaper. Viewers understand that the image of the grim reaper is a symbolic representation of death.
NOTE  A Property Descriptor is not provided as an argument to a property decorator due to how property decorators are initialized in TypeScript. This is because there is currently no mechanism to describe an instance property when defining members of a prototype, and no way to observe or modify the initializer for a property. The return value is ignored too. As such, a property decorator can only be used to observe that a property of a specific name has been declared for a class.
Moreover, the use of language is only an abstraction for a color equivalent. The word "red", for example, can cover a wide range of variations from the pure red of the visible spectrum of light. There is not a formalized register of different colors in the way that there is agreement on different notes in music, such as F or C♯. For a painter, color is not simply divided into basic (primary) and derived (complementary or mixed) colors (like red, blue, green, brown, etc.).
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