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Файл:Programming_in_Scala,_2nd_edition.pdf
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- •Contents
- •List of Figures
- •List of Tables
- •List of Listings
- •Foreword
- •Foreword to the First Edition
- •Acknowledgments
- •Introduction
- •A Scalable Language
- •A language that grows on you
- •What makes Scala scalable?
- •Why Scala?
- •Conclusion
- •First Steps in Scala
- •Conclusion
- •Next Steps in Scala
- •Conclusion
- •Classes and Objects
- •Semicolon inference
- •Singleton objects
- •A Scala application
- •Conclusion
- •Basic Types and Operations
- •Some basic types
- •Literals
- •Operators are methods
- •Arithmetic operations
- •Relational and logical operations
- •Bitwise operations
- •Object equality
- •Operator precedence and associativity
- •Rich wrappers
- •Conclusion
- •Functional Objects
- •Checking preconditions
- •Self references
- •Auxiliary constructors
- •Method overloading
- •Implicit conversions
- •A word of caution
- •Conclusion
- •Built-in Control Structures
- •If expressions
- •While loops
- •For expressions
- •Match expressions
- •Variable scope
- •Conclusion
- •Functions and Closures
- •Methods
- •Local functions
- •Short forms of function literals
- •Placeholder syntax
- •Partially applied functions
- •Closures
- •Special function call forms
- •Tail recursion
- •Conclusion
- •Control Abstraction
- •Reducing code duplication
- •Simplifying client code
- •Currying
- •Writing new control structures
- •Conclusion
- •Composition and Inheritance
- •A two-dimensional layout library
- •Abstract classes
- •Extending classes
- •Invoking superclass constructors
- •Polymorphism and dynamic binding
- •Using composition and inheritance
- •Heighten and widen
- •Putting it all together
- •Conclusion
- •How primitives are implemented
- •Bottom types
- •Conclusion
- •Traits
- •How traits work
- •Thin versus rich interfaces
- •Example: Rectangular objects
- •The Ordered trait
- •Why not multiple inheritance?
- •To trait, or not to trait?
- •Conclusion
- •Packages and Imports
- •Putting code in packages
- •Concise access to related code
- •Imports
- •Implicit imports
- •Package objects
- •Conclusion
- •Assertions and Unit Testing
- •Assertions
- •Unit testing in Scala
- •Informative failure reports
- •Using JUnit and TestNG
- •Property-based testing
- •Organizing and running tests
- •Conclusion
- •Case Classes and Pattern Matching
- •A simple example
- •Kinds of patterns
- •Pattern guards
- •Pattern overlaps
- •Sealed classes
- •The Option type
- •Patterns everywhere
- •A larger example
- •Conclusion
- •Working with Lists
- •List literals
- •The List type
- •Constructing lists
- •Basic operations on lists
- •List patterns
- •First-order methods on class List
- •Methods of the List object
- •Processing multiple lists together
- •Conclusion
- •Collections
- •Sequences
- •Sets and maps
- •Selecting mutable versus immutable collections
- •Initializing collections
- •Tuples
- •Conclusion
- •Stateful Objects
- •What makes an object stateful?
- •Reassignable variables and properties
- •Case study: Discrete event simulation
- •A language for digital circuits
- •The Simulation API
- •Circuit Simulation
- •Conclusion
- •Type Parameterization
- •Functional queues
- •Information hiding
- •Variance annotations
- •Checking variance annotations
- •Lower bounds
- •Contravariance
- •Object private data
- •Upper bounds
- •Conclusion
- •Abstract Members
- •A quick tour of abstract members
- •Type members
- •Abstract vals
- •Abstract vars
- •Initializing abstract vals
- •Abstract types
- •Path-dependent types
- •Structural subtyping
- •Enumerations
- •Case study: Currencies
- •Conclusion
- •Implicit Conversions and Parameters
- •Implicit conversions
- •Rules for implicits
- •Implicit conversion to an expected type
- •Converting the receiver
- •Implicit parameters
- •View bounds
- •When multiple conversions apply
- •Debugging implicits
- •Conclusion
- •Implementing Lists
- •The List class in principle
- •The ListBuffer class
- •The List class in practice
- •Functional on the outside
- •Conclusion
- •For Expressions Revisited
- •For expressions
- •The n-queens problem
- •Querying with for expressions
- •Translation of for expressions
- •Going the other way
- •Conclusion
- •The Scala Collections API
- •Mutable and immutable collections
- •Collections consistency
- •Trait Traversable
- •Trait Iterable
- •Sets
- •Maps
- •Synchronized sets and maps
- •Concrete immutable collection classes
- •Concrete mutable collection classes
- •Arrays
- •Strings
- •Performance characteristics
- •Equality
- •Views
- •Iterators
- •Creating collections from scratch
- •Conversions between Java and Scala collections
- •Migrating from Scala 2.7
- •Conclusion
- •The Architecture of Scala Collections
- •Builders
- •Factoring out common operations
- •Integrating new collections
- •Conclusion
- •Extractors
- •An example: extracting email addresses
- •Extractors
- •Patterns with zero or one variables
- •Variable argument extractors
- •Extractors and sequence patterns
- •Extractors versus case classes
- •Regular expressions
- •Conclusion
- •Annotations
- •Why have annotations?
- •Syntax of annotations
- •Standard annotations
- •Conclusion
- •Working with XML
- •Semi-structured data
- •XML overview
- •XML literals
- •Serialization
- •Taking XML apart
- •Deserialization
- •Loading and saving
- •Pattern matching on XML
- •Conclusion
- •Modular Programming Using Objects
- •The problem
- •A recipe application
- •Abstraction
- •Splitting modules into traits
- •Runtime linking
- •Tracking module instances
- •Conclusion
- •Object Equality
- •Equality in Scala
- •Writing an equality method
- •Recipes for equals and hashCode
- •Conclusion
- •Combining Scala and Java
- •Using Scala from Java
- •Annotations
- •Existential types
- •Using synchronized
- •Compiling Scala and Java together
- •Conclusion
- •Actors and Concurrency
- •Trouble in paradise
- •Actors and message passing
- •Treating native threads as actors
- •Better performance through thread reuse
- •Good actors style
- •A longer example: Parallel discrete event simulation
- •Conclusion
- •Combinator Parsing
- •Example: Arithmetic expressions
- •Running your parser
- •Basic regular expression parsers
- •Another example: JSON
- •Parser output
- •Implementing combinator parsers
- •String literals and regular expressions
- •Lexing and parsing
- •Error reporting
- •Backtracking versus LL(1)
- •Conclusion
- •GUI Programming
- •Panels and layouts
- •Handling events
- •Example: Celsius/Fahrenheit converter
- •Conclusion
- •The SCells Spreadsheet
- •The visual framework
- •Disconnecting data entry and display
- •Formulas
- •Parsing formulas
- •Evaluation
- •Operation libraries
- •Change propagation
- •Conclusion
- •Scala Scripts on Unix and Windows
- •Glossary
- •Bibliography
- •About the Authors
- •Index
Section 28.9 |
Chapter 28 · Working with XML |
668 |
Notice all of the lines that try to process white space as if it were a true thermometer record. What you would really like to do is ignore the white space and process only those sub-nodes that are inside a <cctherm> element. You can describe this subset using the pattern <cctherm>{_*}</cctherm>, and you can restrict the for expression to iterating over items that match that pattern:
catalog match {
case <catalog>{therms @ _*}</catalog> =>
for (therm @ <cctherm>{_*}</cctherm> <- therms) println("processing: "+
(therm \ "description").text)
}
processing: hot dog #5 processing: Sprite Boy
28.9 Conclusion
This chapter has only scratched the surface of what you can do with XML. There are many other extensions, libraries, and tools you could learn about, some customized for Scala, some made for Java but usable in Scala, and some language-neutral. What you should walk away from this chapter with is how to use semi-structured data for interchange, and how to access semistructured data via Scala’s XML support.
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