Odersky M. Programming in Scala
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Index 731
in match expressions, 163
used to initialize a field to its
default value, 392
_
*
(underscore asterisk)
in XML pattern matching, 550
repeated parameter, 189
sequence wildcard pattern, 523
_1, _2, etc.(tuple accessors), 80
_= (underscore equals)
in setter method names, 390
^ (exclusive-or)
on integral types, 121
^^ (result conversion, or
“eyebrows”)
parser combinator, 651
~ (bitwise complement)
on integral types, 121
~ (sequential composition, or
“squiggle”)
parser combinator, 651, 660
~! (committed sequential
composition)
parser combinator, 668
~> (sequential composition right)
parser combinator, 652, 661
<~ (sequential composition left)
parser combinator, 652, 661
\ (extract)
on class Elem, 546
\\ (deep extract)
on class Elem, 546
{} (curly braces)
and variable scope, 167
in class definitions, 130
in imports, 270
in XML literals, 542–543
in XML patterns, 549
instead of parentheses in
method invocations, 203
instead of parentheses in for
expressions, 157
‘ (back tick)
in identifiers, 143
| (alternative composition)
parser combinator, 661
| (alternative composition)
parser combinator, 652
| (bitwise-or)
on integral types, 121
|| (logical-or)
on class Boolean, 120
A
Abelson, Harold, 393, 506
abs method
on class Double (via
RichDouble), 128
on class Int (via RichInt),
139, 240
abstract members, 435
abstract modifier
not needed on abstract methods,
fields, or types, 211, 435
on classes, 210
with override modifier on
members of traits, 256
abstract types, 447
access modifiers, 273–278
accessor methods, 390
Actor trait, 608
methods
! (message send), 43, 610
actor, 610
act, 608
loop, 615
react, 614
receiveWithin, 613
receive, 611
start, 609
actors, 43, 377, 607–641, 677
addString method
on class List, 340
Aho, Alfred, 506, 668n
aliases
AnyRef for Object, 240
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Index 732
int for Int, etc., 108
type, 436
aliasing
this, 659
object, see defensive copies
alphabetic versus symbolic names,
656
alternatives
catch-all, 298
definition of, 709
in match expressions, 163, 296
in catch clauses, 161
in partial function literals, 315
annotations
and reflection, 600
applied to expressions, 534
arguments to, 534
@BeanProperty, 537
@deprecated, 533
in meta-programming, 533
in testing, 285
Java-specific, 597
@serializable, 536, 598
@SerialVersionUID, 536
standard, 535
syntax of, 534
@Test
in JUnit 4, 600
in TestNG, 286
@throws, 598
@transient, 537
type, 40, 54, 60
for debugging, 358
@unchecked, 312, 401, 534
variance, 418
@volatile, 536
anonymous classes, 439
anonymous functions, see function
literals
ANTLR, 642
Any class, 238
in Scala class hierarchy
diagram, 239
AnyRef class, 238
as alias of Object, 240
in Scala class hierarchy
diagram, 239
AnyVal class, 238
in Scala class hierarchy
diagram, 239
application
function to arguments, 181
partial function, 181, 343
Application trait, 105, 672
applications, Scala, 102–105
apply method
called with parentheses, 73
in extractors, 518
on Array
class, 73
object, 75
on List
class, 338
object, 76, 351, 525
on Map
traits, 372
on Map
objects, 85
traits, 371
on Set objects, 81
on trait PartialFunction, 317
on FunctionN traits, 177
args variable
in scripts, 65
arguments
command line, in scripts, 65
variable length, 188
versus parameters, 717
arithmetic operations (+, -,
*
, /, %)
on numeric types, 118–119
Array class, 362
ArrayBuffer class, 364
arrays, 227, 362
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Index 733
accessed with () not [], 73
cloning, 621
converting to lists, 382
creating and initializing, 75
passing elements as arguments
with _
*
, 189
quick introduction, 72–75
asInstanceOf method
on class Any, 304
assert method
on object Predef, 88, 279
AssertionError class, 279
assertions, 279–281
assignment
result is unit value, 153
associativity, 126–127
right versus left, 77, 126
asynchronous messages, 619
attributes
XML, 541, 546
automatic
boxing, 241
conversion, see implicit
conversion
imports, 272
auxiliary constructors, 136–137
B
backtracking, 667
base classes, see superclasses
BDD, see behavior-driven
development
BeanProperty annotation, 537,
556n
Beck, Kent, 284
behavior-driven development, 286
Beust, Cédric, 285
BigInt class, 41
BigInteger class, 42
Bison, 642
bitwise operations, on integral types
logical (&, |, ^, ~), 121
shift (<<, >>, >>>), 122
blank finals (Java)
not in Scala, 392
Bloch, Joshua, 569n, 582n, 590n
blocks, definition of, 710
Boolean class, 108, 120
boolean literals, 115
bottom types, 243
bound variables, 157, 184
boxing, of value types, 241
Bracha, Gilad, 506
break keyword (Java)
living without, 165
not in match expressions, 164
ButtonClicked class, 676
by-name parameters, 206, 399
by-value parameters, 662
Byte class, 107, 591
C
C language, 47
parser generators, 642
C++ language, 47, 86
C# language, 86
enumerations, 452
properties, 392
static extension methods, 465
Callahan, Harry, 620
camel casing, 141
capitalization, of identifiers, 141
capitalize method
on class Int (via RichInt), 128
case classes, 294–295
and actors, 621
versus extractors, 526–527
cases, see alternatives
casting, see also toInt, toChar, etc.
with asInstanceOf, 304
with typed patterns (the
preferred style), 303
catch clauses, 161
Cathedral and the Bazaar, The
(Raymond), 41
Char class, 107, 591
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Index 734
character encoding
in XML, 548
character literals, 111
escape sequences, 112
checked exceptions, 161, 598
Church, Alonzo, 46
Class class, see classOf method
class hierarchy diagram
for collections, 360
for iterators, 361
for lists, 488
for maps, 84
for Scala, 239
for sets, 82
class parameters, 130
initialization order compared to
abstract fields, 441
not legal on singleton objects,
102
used to implement abstract
fields, 490
classes, 93–95
abstract, 210
annotating, 534
anonymous, 439
case, 294–295
companion, 100
generic, 410
inner, see inner classes
nesting of, 231
private, 415
sealed, 310–312
classOf method
on object Predef, 283, 599
clear method
on mutable Set trait, 370
closures, 184–188, 197
versus Java’s inner classes,
186n
code duplication
reducing, 52, 194–200
collections, 359–386
class hierarchy diagram, 360
combinators, 210
companion classes, 100
companion objects, 75, 100
and factory methods, 414
and implicit conversion, 469
visibility, 277
compare method
of trait Ordered, 253, 431
compatibility, Scala with Java, 39,
48–49
compiler errors
’;’ expected but ’,’ found, 204
. . . is already defined as . . . , 308
. . . is not a legal prefix for a
constructor, 452
overloaded method value
. . . with alternatives
. . . cannot be applied to
. . . , 146
class . . . is abstract; cannot be
instantiated, 211
class . . . needs to be abstract,
since method . . . in class
. . . of type . . . is not
defined, 447
class type required, 456
constructor . . . cannot be
accessed in . . . , 414
covariant type . . . occurs in
contravariant position in
type . . . of parameter of
setter . . . , 431
covariant type . . . occurs in
contravariant position in
type . . . of value . . . , 419,
422
error overriding method . . . in
class . . . of type . . . method
. . . cannot override final
member, 224
error overriding method . . . in
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Index 735
class . . . of type . . . method
. . . needs ’override’
modifier, 221
illegal inheritance from final
class, 225
inferred type arguments . . . do
not conform to method
. . . type parameter bounds
. . . , 433
method . . . overrides nothing,
220, 447
missing arguments for method
. . . follow this method with
’_’ if you want to treat it as
a partially applied
function, 184
no implicit argument matching
parameter type . . . was
found, 381, 476, 478
not found: value . . . , 114, 184
overloaded method value
. . . with alternatives
. . . cannot be applied to
. . . , 474
pattern is unchecked since it is
eliminated by erasure, 584
reassignment to val, 61, 378
trait . . . takes type parameters,
417
type mismatch, 188, 381, 421,
449, 450, 463, 471, 485,
565, 566
unreachable code, 310
value . . . is not a member of . . . ,
134, 442
compiler warnings
match is not exhaustive, 316,
401
non variable type-argument
. . . in type pattern is
unchecked since it is
eliminated by erasure, 305,
584
there were unchecked warnings;
re-run with -unchecked for
details, 305
Compilers: Principles, Techniques,
and Tools (Aho, et. al.),
670n
compiling, 104
complexity, managing, 51
Component class, 673
composition, 216, 226
mixin, see mixin composition
concat method
on object List, 354
conciseness
Scala versus Java, 49–51
concurrency
actors model, 43, 607–641
and testing, 608
shared data and locks, 608
shared-nothing, 608
ConcurrentHashMap class, 619
configuring
to wire modules together, 554
with Scala code, 565
cons (::) method
on class List, 76, 328, 412, 489
right associativity of, 77
short for construct, 489
Console object, 89
constant patterns, 296, 299
constants, 142
constructor patterns, 296, 301
constructors, 71
auxiliary, 136–137
in Java versus Scala, 131
invoking superclass, 219
primary, 130–132
private, 414
Container trait, 673
contains method
on Map traits, 372
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Index 736
contains method
on Set traits, 370
contents property
on trait Container, 673
context-free grammars, 643
continue keyword (Java)
living without, 165
contravariance, 418, 426–429
control abstraction, 47, 194–208
conventions, identifier capitalization,
141
conversion
implicit, 49, 465
to target type, 467
copyToArray method
on class List, 340
count method
on class List, 78
covariance, 418
of arrays in Java, 420
of function result type, 427
of lists, 328, 492
creating and initializing
arrays, 75
lists, 76
maps, 85
objects with factories, 75, 229
objects with new, 93
sets, 81
singleton objects, 102
tuples, 80
curly braces
and variable scope, 167
in class definitions, 130
in imports, 270
in XML literals, 542–543
in XML patterns, 549
instead of parentheses in
method invocations, 203
instead of parentheses in for
expressions, 157
currying, 200–202, 342
D
data structures
fully persistent, 411
semi-structured, 539
deadlock, 43, 608
deafTo method
on Reactor, 676
declarations, versus definitions, 712
decrementing
with -= 1, not --, see
incrementing
def keyword, 62, 93
annotating, 534
default values
of fields, 392
defensive copies, 131
definitions, versus declarations, 712
dependency injection, 554
deprecated annotation, 533, 597
dequeue method
on class Queue, 365
DeRemer, Frank, 553n
derived classes, see subclasses
deserialization
XML, 547
Design Patterns (Gamma, et. al.),
297n
Dijkstra, Edsger, 54
Dirty Harry, 620
divide and conquer principle, 333
do-while loops, 152
domain objects, 555
Domain-Driven Design (Evans),
555n
domain-specific languages, 707
a little language for digital
circuits, 393
and implicit conversions, 473
defining an external DSL with
parser combinators,
642–652
embedded in Scala, xxvii
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Index 737
in Smalltalk and Lisp, 56
parser combinators as an
internal DSL, 642
rich wrappers and internal
versus external DSLs, 475
Double class, 107
downloading
Scala, 58
source code for book examples,
xxxvii
drop method
on class List, 78, 337
dropRight method
on class List, 78
dropWhile method
on class List, 346
DSLs, see domain-specific languages
dynamic
binding, 222, 248
typing, xxvii, 53, 114
E
Eastwood, Clint, 620
Eckel, Bruce, 226n
Eclipse IDE, 58, 671
EditDone class, 681
Effective C++ (Meyers), 226n
Effective Java, Second Edition
(Bloch), 569n, 582n, 590n
efficiency
and hash consing, 242
and trait ScalaObject, 241
of abstract classes versus traits,
263n, 294n
of arrays, 75, 362
of case classes versus
extractors, 526
of class ListBuffer, 363, 494
of fold left and right, 349
of functional on the outside,
imperative on the inside
approach, 497
of immutable objects, 131
of lists, 361
of LL(1) versus backtracking
parsers, 669
of looping versus recursion, 189
of maps, 373
of merge versus insertion sort,
341
of sets, 373
of tail versus non-tail recursion,
495
of thread creation and
switching, 613
of value types, 59, 75, 238, 595
Eiffel language, 56
Elem class, 541, 546
Elem type
in trait Parsers, 657
elements method
on class List, 341
on trait Iterable, 359
elements, XML, 540–541
else clauses, 150
embedded DSLs, see
domain-specific languages
empty method
on Map objects, 369, 373
on Set objects, 369, 370
empty-paren methods, 212
enclosing instances, see inner classes
enqueue method
on class Queue, 365
ensuring method
on object Predef, 280
entities, 556
enum keyword (Java), see
Enumeration class
Enumeration class, 452
eq method
on class AnyRef, 124, 243, 568
equality, see also equals method
!= (not equals) method
on class Any, 123, 237
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Index 738
== (equals) method
on class Any, 123, 237, 568
=== (triple equals) method
in ScalaTest suites, 282
eq method
on class AnyRef, 124, 243,
568
in Scala versus Java, 124
in-depth treatment, 568–593
ne method
on class AnyRef, 124, 243
quick introduction, 123–124
value versus reference, 124
equals method, see also equality
generated for case classes, 295
on class Any, 124, 237, 568–593
contract of, 575
recipe for writing, 587–590
erasure, 306
and pattern matching, 584
Erlang language, 43–44, 47, 86
and actors, 619
errata, viewing and reporting, xxxvii
errors, see also compiler errors
handling with exceptions,
159–163
in parsing, 665–667
preventing, 87
escape sequences, for character
literals, 112
Evans, Eric, 555n
event handling, 676–679, 702
event listeners, 676
event sources, 676
example code, for book
downloading, xxxvii
license of, xxxvii
exception handling, 159–163
and checked exceptions,
598–599
existential types, 586, 602–605
exists method
on class List, 78, 199, 347
on class RichString, 367
exists2 method
on object List, 354
extends keyword, 214
external DSLs, see domain-specific
languages
extractors, 516–520
and injections, 520
extractor pattern, 331, 520
F
F# language, 47, 57
factory methods, 75, 456
factory objects, 229
Failure class, 658
false value, 115
fields, 93–95
abstract, 441
defining, 139
initializing to default values
with an underscore, 392
overriding, 216–217
parametric, 134, 217
pre-initialized, 441
private, 95, 138
FileReader class, 649
files
ensuring closed with finally,
162
opening, 89
reading lines from, 89
filter method
on class List, 78, 345
translating for expressions to
invocations of, 501
filters
in for expressions, 156, 502
final modifier, 224
on variables (Java), see vals
finally clauses, 161
find method
on class List, 346
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Index 739
findAllIn method
on class Regex, 529
findFirstIn method
on class Regex, 529
findPrefixOf method
on class Regex, 529
first-order methods
on class List, 332–343
flatMap method
on class List, 344
translating for expressions to
invocations of, 501
flatten method
on object List, 349, 353
Flex, 642
Float class, 107
floating-point literals, 110
floatingPointNumber method
in trait JavaTokenParsers,
644, 650
fold
left, 348
right, 348
foldLeft method
on class List, 349
foldRight method
on class List, 349
for expressions, 69, 154, 501
and extractors, 531
and XML patterns, 550–552
notation, 506
translated before type checking,
513
types valid after ->, 513
using patterns in, 317, 502
for loops, 511
forall method
on class List, 78, 347
forall2 method
on object List, 354
foreach method
on class Array, 68
on class List, 78, 345
translating for expressions to
invocations of, 501
formatted method
on Any (via StringAdd), 459
formatting strings, 459
forSome keyword, 603
Fortran language, 42
Fowler, Martin, 554n
free variables, 184
fsc (fast Scala compiler), 104
fully qualified names, 83
function literals
and closures, 186
for partial functions, 314
placeholder syntax, 180, 197
syntax of, 69
underscores in, 180, 197
versus function values, 177
function values, 177, 196
and closures, 186
functional programming, 39, 46–48,
129
lazy initialization, 446
main ideas of, 47
functional style, 81
combining with imperative
style, 497
in parsing, 657
methods without side effects, 75
recognizing, 86
refactoring functional style to,
170
functions, see also methods
basic form of, 63
first-class, 47, 177
higher-order, 194
local, 175
partial, 314–317
partially applied, 181, 343
predicates, 51
procedures, 97
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Index 740
pure, 213
recursive, 189
tail recursive, 190
G
Gamma, Erich, 284, 297n
generator, in for expressions, 502
generic types, 410, 417
getLines method
on object Source, 89
getter methods, 390, 423, 438, 673
Goetz, Brian, 619n
Gosling, James, 420, 506
graphical user interfaces, see user
interfaces
Groovy language, xxvii
“Growing a language” (Steele), 41n
GUI programming, see user
interfaces
Guice, 554
H
Haller, Philipp, 623
handlers, exception, see catch
clauses
hash consing, 242
hashCode method
caching, 592
generated for case classes, 295
if overriding equals, 572–573
on class Any, 237
contract of, 573
recipe for writing, 590–592
HashMap class
in class hierarchy diagram, 84
HashSet class, 81
creating and initializing
immutable, 83
in class hierarchy diagram, 82
Haskell language, 42, 47, 86
as a lazy functional language,
446
hasNext method
on trait Iterator, 360
head method
on class List, 79, 329, 488
Hejlsberg, Anders, 433
Hibernate, 556
hiding
names in import clauses, 271
names in nested packages, 266
variables in nested blocks, 169
higher-kinded types, see http://
booksites.artima.com/
programming_in_scala
higher-order functions, 194
higher-order methods
on class List, 343–351
I
identifiers, 141–143
alphanumeric, 141
capitalization conventions for,
141
literal (with back ticks), 143
mixed, 143
operator, 142
identity
function, for implicit
conversions, 483
of objects, testing with eq
method, 568
idioms, see patterns and idioms
if expressions, 63, 67, 150–151
immutability, 47
as functional style, 75
selecting mutable versus
immutable collections, 377
trade-offs, 131
imperative style, 81
combining with functional
style, 497
recognizing, 86
refactoring to functional style,
170
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