old relationships between functional and object-oriented program‐ ming. There's only so much you . read because it obscures the programmer's intent. We don't want to . of assets and render the BalanceSheet to a PDF report. If the imple‐. echecs16.info - Download as PDF File .pdf), hard to read because it obscures the programmer's intent. but first let's take a. Functional Programming for the Object Oriented Programmer. 24 August This book, written by Brian Marick, is important. Indeed, it may.
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Functional Programming for the Object-Oriented Programmer. Brian Marick For more about what the book covers, see the sample PDF. Once upon a time, object-oriented programming was a radical . In the PDF version, links within a book appear as colored text, and links to. Functional Programming for the Object-Oriented Programmer by Brian Marick ( echecs16.info) echecs16.info~rwh/plbook/echecs16.info
Shelves: software-development , quit-reading This book tries to explain functional programming with a lot of code examples using Clojure. Although the first chapter introduces the reader to Clojure which was very enlighting , the fact that this was my first adventure into the language got constantly in my way of understanding the bigger picture. After reading this book halfway through, I was totally lost. Perhaps picking up another book on Clojure before reading this book is a much better approach in order to get the most out of it. Jun 07, Nathan rated it really liked it A great intro to functional programming. The overall organization is good, and I liked the level of detail for an introductory book.
It has a few logically different objects which communicate with each other — according to the rules defined in the program. Encapsulation is achieved when each object keeps its state private, inside a class. Instead, they can only call a list of public functions — called methods.
So, the object manages its own state via methods — and no other class can touch it unless explicitly allowed. If you want to communicate with the object, you should use the methods provided. There are people and there is a cat. They communicate with each other. It may look like this: You can feed the cat.
It also has a private method meow. What they can do is defined in the public methods sleep , play and feed. Each of them modifies the internal state somehow and may invoke meow. Thus, the binding between the private state and public methods is made. This is encapsulation. Abstraction Abstraction can be thought of as a natural extension of encapsulation. In object-oriented design, programs are often extremely large. And separate objects communicate with each other a lot.
So maintaining a large codebase like this for years — with changes along the way — is difficult. Abstraction is a concept aiming to ease this problem. Applying abstraction means that each object should only expose a high-level mechanism for using it. This mechanism should hide internal implementation details. It should only reveal operations relevant for the other objects. Think — a coffee machine.
It does a lot of stuff and makes quirky noises under the hood. But all you have to do is put in coffee and press a button. Preferably, this mechanism should be easy to use and should rarely change over time. Another real-life example of abstraction?
Think about how you use your phone: Cell phones are complex. But using them is simple. You interact with your phone by using only a few buttons. What better way to explain and expose functional programming to an OO programmer than to build an object system in a functional language? And what better language to build such an object system than Clojure? So he chose the simplest one to learn. He also realized that teaching the language would distract from the purpose of the book.
So he strikes a brilliant compromise: He presents the barest minimum of the language he can get by with, and then gets right on with the business of describing functional programming.
The technique is very effective; though many Clojure programmers will find the language primitives he constrains himself to a wee bit frustrating. A final point that I think is worth reflecting on is that in the context of Java 8. Informally we can think 14 Chapter 2: Then q y should be true for objects y of type S where S is a subtype of T.
There is no internal state to mutate. Within a modern Agile developer environment. Immutable objects are also of particular interest because they are inherently thread-safe. Functional programming tends to take a different perspective to LSP.
We might define our worker interface as follows: Where parent always stuck left or maintained something. We can split out that property into four distinct areas: The Interface-Segregation Principle The dependency of one class to another one should depend on the smallest possible interface In order to properly understand the interface-segregation principle. Where the parent worked. Where the parent caused an effect.
This is shown in Example The relationship is explicit and based upon the name of the class. As time passes.
Now the interesting point about this example is that it all relates to subtyping. Our robots also do work in the factory. This applies equally to interfaces as well as classes. Parsing the headings out of a file class AssemblyWorker implements Worker class Manager implements Worker class Robot implements Worker When the compiler comes to check whether a parameter argument is type checked.
Most statically typed object-oriented languages. This means that for a class called Foo to extend a class called Bar. In our worked example. The alternative approach is called structural subtyping.
The Dependency-Inversion Principle Abstractions should not depend on details. So if you call a method called getFoo on a variable. If we think about this hypothetical example in a language which uses structural subtyping. The duck typing in languages like Ruby and Python is a dynamically typed variant of structural subtyping. A minimal interface is automatically inferred by the compiler from the use of these parameters. The Dependency-Inversion Principle The key is that the parameter worker has no explicit type.
On of the ways in which we can make rigid and fragile programs that are resistant to change is by coupling high-level business logic and low-level code designed to glue modules together. Dependencies In this system.
Figure This allows us to reuse the high-level code in a way that is abstract of the details upon which it depends.
Our application takes in a sequence of electronic business cards as input and accumulates our address book in some storage mechanism. This is because these are two different concerns that may change over time. In this case. This is the dependency- inversion principle at work. Our method is going to extract the headings from a file by reading the file.
We can therefore easily reuse them in another system. In order to give ourselves the flexibility to change these components within our system. In the context of lambda expressions. The implementation of our accumulation module depends upon these abstractions. We can pass in the specific details of these implementations at runtime. The code looks like Example We can also change them.
What we really want to do is write some code that finds the headings and delegates the details of a file to another method. A Stream is much safer and less open to abuse. This approach. This exception then gets thrown in the event of a problem. To summarize. Summary The handler function represents the body of whatever code we want to use with this function. We can easily use them with lambda expressions.
We talked about how the single-responsibility principle means that classes should only have a single reason to change. This is wrapped up in BufferedReader. Finally we talked about how higher-order functions were really a form of dependency inversion. The interface-segregation principle encourages us to minimize the dependency on large interfaces that have multiple responsibilities.
In functional programming. In all cases. No inheritance. The Command Pattern A command object is an object that encapsulates all the information required to call another method later.
Patterns document reusable templates that solve common problems in software architecture. There are four classes that take part in the command pattern. In this section. In a sense. The command pattern is a way of using this object in order to write generic code that sequences and executes methods based on runtime decisions.
This is our receiver. We want to implement macro functionality—that is. All these classes need to do is call a single method on our Editor and wrap this call into our Action interface. Example and Example are our command objects.
This is the interface that all our command objects implement Example As a lazy programmer. This class can record actions and run them as a group. I love the ability to define common workflows as macros. We use a List to store the sequence of actions and then call forEach in order to execute each Action in turn.
We can then just run the macro. Example is our invoker. Example shows how to use our Macro class without these command classes and with lambda expressions instead. How do lambda expressions help? This whole pattern becomes a lot simpler with lambda expressions because we can entirely dispense with these classes. The Macro object is our client code and is shown in Example They have the compress method. We could have chosen to use that in our macro class.
First we need to define the API for our strategy see Figure Strategy Pattern The strategy pattern is a way of changing the algorithmic behavior of software based upon a runtime decision. An example algorithm we might want to encapsulate is compressing files.
The returned OutputStream is a compressed version of the input see Example How you implement the strategy pattern depends upon your circumstances.
There is already a functional interface with the same structure as our interface Action in core Java— Runnable. The Strategy Pattern Example Strategy Pattern This has a compress method on it that takes input and output files and writes a compressed version of the input file to the output file.
As with the command pattern discussed earlier. The command pattern is all about first-class functions. This is the great win about being able to combine the functional and object- oriented world view: