What do all of Scala s symbolic operators mean

Question

Scala syntax has a lot of symbols  Since these kinds of names are difficult to find using search engines  a comprehensive list of them would be helpful   What are all of the symbols in Scala  and what does each of them do   In particular  I d like to know about - gt              lt             and

User · Answer

lt   is just like you would  read  it   less than or equals   So it s a mathematical operator  in the list of  lt   is less than     gt   is greater than        equals        is not equal     lt    is less than or equal    and  gt    is greater than or equal     This must not be confused with   gt  which is kind of a double right-hand arrow  used to separate the argument list from the body of a function and to separate the testing condition in pattern matching  a case block  from the body executed when a match occurs  You can see example of this in my previous two answers  First  the function use   coll map tup   gt  tup  2 reverse    which is already abbreviated as the types are omitted  The follow function would be     function arguments         function body  tup  Tuple2 Int  String     gt  tup  2 reverse   and the pattern matching use   def extract2 l  List Int     l match         if l matches Nil    return  empty     case Nil              gt   empty        etc     case    head  Nil     gt   exactly one element      head             etc     case    head  tail    gt   more than one element

User · Answer

Oohoo so you want an exhaustive answer  Here s a fun  hopefully complete  and rather lengthy list for you    http   jim-mcbeath blogspot com 2008 12 scala-operator-cheat-sheet html  Disclaimer - the post was written in 2008 so may be a little out of date     AbstractActor    Actor    Sends msg to this actor and immediately        Proxy   Actor    Sends msg to this actor  asynchronous     Channel    Sends a message to this Channel    OutputChannel    Sends msg to this       Proxy    Sends msg to this        Any    o    arg0 is the same as   o     arg0       AnyRef    Boolean    Byte    Char    Double    Float    Int    Long    Short    AbstractActor    Actor    Sends msg to this actor and awaits reply        Channel    Sends a message to this Channel and        Proxy   BigInt    Remainder of BigInts   Byte   Char   Double   Float   Int   Long   Short   Elem    Returns a new element with updated attributes  resolving namespace uris from this element s scope       amp  amp  amp  Parsers Parser  amp  amp  Boolean  amp   NodeBuffer    Append given object to this buffer  returns reference on this NodeBuffer      amp  BigInt    Bitwise and of BigInts  amp  Boolean  amp  Byte  amp  Char  amp  Enumeration Set32    Equivalent to   for bit sets       amp  Enumeration Set64    Equivalent to   for bit sets       amp  Enumeration SetXX    Equivalent to   for bit sets       amp  Int  amp  Long  amp  Short  amp   BigInt    Bitwise and-not of BigInts  Returns a BigInt whose value is  this  amp   that    amp   Enumeration Set32    Equivalent to - for bit sets       amp   Enumeration Set64    Equivalent to - for bit sets       amp   Enumeration SetXX    Equivalent to - for bit sets       gt  gt  gt  Byte  gt  gt  gt  Char  gt  gt  gt  Int  gt  gt  gt  Long  gt  gt  gt  Short  gt  gt  BigInt     Signed  rightshift of BigInt  gt  gt  Byte  gt  gt  Char  gt  gt  Int  gt  gt  Long  gt  gt  Short  gt  gt  Parsers Parser    Returns into fq   gt  gt  Parsers Parser    Returns into fq   gt  BigDecimal    Greater-than comparison of BigDecimals  gt  BigInt    Greater-than comparison of BigInts  gt  Byte  gt  Char  gt  Double  gt  Float  gt  Int  gt  Long  gt  Ordered  gt  PartiallyOrdered  gt  Short  gt   BigDecimal    Greater-than-or-equals comparison of BigDecimals  gt   BigInt    Greater-than-or-equals comparison of BigInts  gt   Byte  gt   Char  gt   Double  gt   Float  gt   Int  gt   Long  gt   Ordered  gt   PartiallyOrdered  gt   Short  lt  lt  BigInt    Leftshift of BigInt  lt  lt  Byte  lt  lt  Char  lt  lt  Int  lt  lt  Long  lt  lt  Short  lt  lt  Buffer    Send a message to this scriptable object   lt  lt  BufferProxy    Send a message to this scriptable object   lt  lt  Map    Send a message to this scriptable object   lt  lt  MapProxy    Send a message to this scriptable object   lt  lt  Scriptable    Send a message to this scriptable object   lt  lt  Set    Send a message to this scriptable object   lt  lt  SetProxy    Send a message to this scriptable object   lt  lt  SynchronizedBuffer    Send a message to this scriptable object   lt  lt  SynchronizedMap    Send a message to this scriptable object   lt  lt  SynchronizedSet    Send a message to this scriptable object   lt  BigDecimal    Less-than of BigDecimals  lt  BigInt    Less-than of BigInts  lt  Byte  lt  Char  lt  Double  lt  Float  lt  Int  lt  Long  lt  Ordered  lt  PartiallyOrdered  lt  Short  lt  OffsetPosition    Compare this position to another  by first comparing their line numbers       lt  Position    Compare this position to another  by first comparing their line numbers       lt   BigDecimal    Less-than-or-equals comparison of BigDecimals  lt   BigInt    Less-than-or-equals comparison of BigInts  lt   Byte  lt   Char  lt   Double  lt   Float  lt   Int  lt   Long  lt   Ordered  lt   PartiallyOrdered  lt   Short  lt   Parsers Parser    A parser combinator for sequential composition which keeps only the left result    Enumeration SetXX    Set    Intersect  It computes an intersection with set that         Set    This method is an alias for intersect        BigDecimal    Multiplication of BigDecimals   BigInt    Multiplication of BigInts   Byte   Char   Double   Float   Int   Long   Short   Set   RichString    return n times the current string   Parsers Parser    Returns a parser that repeatedly parses what this parser parses  interleaved with the  sep  parser        Parsers Parser    Returns a parser that repeatedly parses what this parser parses   Parsers Parser    Returns a parser that repeatedly parses what this parser parses  interleaved with the  sep  parser        Parsers Parser    Returns a parser that repeatedly parses what this parser parses  interleaved with the  sep  parser    Parsers Parser    Returns a parser that repeatedly parses what this parser parses     ArrayBuffer    Prepends a number of elements provided by an iterable object         Buffer    Prepends a number of elements provided by an iterable object         BufferProxy    Prepends a number of elements provided by an iterable object         SynchronizedBuffer    Prepends a number of elements provided by an iterable object        Array    Returns an array consisting of all elements of this array followed        Enumeration SetXX    Iterable    Appends two iterable objects     IterableProxy    Appends two iterable objects     Iterator    Returns a new iterator that first yields the elements of this        List    Appends two list objects     RandomAccessSeq    Appends two iterable objects     RandomAccessSeqProxy    Appends two iterable objects     Seq    Appends two iterable objects     SeqProxy    Appends two iterable objects     IntMap    Add a sequence of key value pairs to this map     LongMap    Add a sequence of key value pairs to this map     Map    Add a sequence of key value pairs to this map     Set    Add all the elements provided by an iterator        Set    Add all the elements provided by an iterator to the set     SortedMap    Add a sequence of key value pairs to this map     SortedSet    Add all the elements provided by an iterator        Stack    Push all elements provided by the given iterable object onto        Stack    Push all elements provided by the given iterator object onto        TreeHashMap    TreeHashMap    Add a sequence of key value pairs to this map     Collection    Operator shortcut for addAll     Set    Operator shortcut for addAll     ArrayBuffer    Appends two iterable objects     Buffer    Appends a number of elements provided by an iterable object        Buffer    Appends a number of elements provided by an iterator        Buffer    Appends two iterable objects     BufferProxy    Appends a number of elements provided by an iterable object        Map    Add a sequence of key value pairs to this map     MapProxy    Add a sequence of key value pairs to this map     PriorityQueue    Set    Add all the elements provided by an iterator        SynchronizedBuffer    Appends a number of elements provided by an iterable object        RichString    Appends two iterable objects     RichStringBuilder    Appends a number of elements provided by an iterable object        RichStringBuilder    Appends two iterable objects      Map    Add a sequence of key value pairs to this map      MapWrapper    Add a sequence of key value pairs to this map      ArrayBuffer    Appends a number of elements in an array     ArrayBuffer    Appends a number of elements provided by an iterable object         ArrayStack    Pushes all the provided elements onto the stack      Buffer    Appends a number of elements in an array     Buffer    Appends a number of elements provided by an iterable object         Buffer    Appends a number of elements provided by an iterator     BufferProxy    Appends a number of elements provided by an iterable object         Map    Add a sequence of key value pairs to this map      MapProxy    Add a sequence of key value pairs to this map      PriorityQueue    Adds all elements provided by an Iterable object         PriorityQueue    Adds all elements provided by an iterator into the priority queue      PriorityQueueProxy    Adds all elements provided by an Iterable object         PriorityQueueProxy    Adds all elements provided by an iterator into the priority queue      Queue    Adds all elements provided by an Iterable object         Queue    Adds all elements provided by an iterator         QueueProxy    Adds all elements provided by an Iterable object         QueueProxy    Adds all elements provided by an iterator         Set    Add all the elements provided by an iterator         SetProxy    Add all the elements provided by an iterator         Stack    Pushes all elements provided by an Iterable object         Stack    Pushes all elements provided by an iterator         StackProxy    Pushes all elements provided by an Iterable object         StackProxy    Pushes all elements provided by an iterator         SynchronizedBuffer    Appends a number of elements provided by an iterable object         SynchronizedMap    Add a sequence of key value pairs to this map      SynchronizedPriorityQueue    Adds all elements provided by an Iterable object         SynchronizedPriorityQueue    Adds all elements provided by an iterator into the priority queue      SynchronizedQueue    Adds all elements provided by an Iterable object         SynchronizedQueue    Adds all elements provided by an iterator         SynchronizedSet    Add all the elements provided by an iterator         SynchronizedStack    Pushes all elements provided by an Iterable object         SynchronizedStack    Pushes all elements provided by an iterator         RichStringBuilder    Appends a number of elements provided by an iterable object        ArrayBuffer    Prepends a single element to this buffer and return        Buffer    Prepend a single element to this buffer and return        BufferProxy    Prepend a single element to this buffer and return        ListBuffer    Prepends a single element to this buffer  It takes constant        ObservableBuffer    Prepend a single element to this buffer and return        SynchronizedBuffer    Prepend a single element to this buffer and return        RichStringBuilder    Prepend a single element to this buffer and return        BufferWrapper    Prepend a single element to this buffer and return        RefBuffer    Prepend a single element to this buffer and return       BigDecimal    Addition of BigDecimals   BigInt    Addition of BigInts   Byte   Char   Double   Enumeration SetXX    Create a new set with an additional element    Float   Int   List   Long   Short   EmptySet    Create a new set with an additional element    HashSet    Create a new set with an additional element    ListSet Node    This method creates a new set with an additional element    ListSet    This method creates a new set with an additional element    Map   Map    Add a key value pair to this map    Map    Add two or more key value pairs to this map    Queue    Creates a new queue with element added at the end       Queue    Returns a new queue with all all elements provided by       Set    Add two or more elements to this set    Set    Create a new set with an additional element    Set1    Create a new set with an additional element    Set2    Create a new set with an additional element    Set3    Create a new set with an additional element    Set4    Create a new set with an additional element    SortedMap    Add a key value pair to this map    SortedMap    Add two or more key value pairs to this map    SortedSet    Create a new set with an additional element    Stack    Push all elements provided by the given iterable object onto       Stack    Push an element on the stack    TreeSet    A new TreeSet with the entry added is returned    Buffer    adds  quot a quot  from the collection  Useful for chaining    Collection    adds  quot a quot  from the collection  Useful for chaining    Map    Add a key value pair to this map    Set    adds  quot a quot  from the collection  Useful for chaining    Buffer    Append a single element to this buffer and return       BufferProxy    Append a single element to this buffer and return       Map    Add a key value pair to this map    Map    Add two or more key value pairs to this map    MapProxy    Add a key value pair to this map    MapProxy    Add two or more key value pairs to this map    ObservableBuffer    Append a single element to this buffer and return       PriorityQueue   Set    Add a new element to the set    Set    Add two or more elements to this set    SynchronizedBuffer    Append a single element to this buffer and return       Parsers Parser    Returns a parser that repeatedly  at least once  parses what this parser parses    Parsers Parser    Returns a parser that repeatedly  at least once  parses what this parser parses     Collection    adds  quot a quot  from the collection     Map    Add a key value pair to this map     ArrayBuffer    Appends a single element to this buffer and returns        ArrayStack    Alias for push     BitSet    Sets i-th bit to true         Buffer    Append a single element to this buffer     BufferProxy    Append a single element to this buffer     HashSet    Add a new element to the set     ImmutableSetAdaptor    Add a new element to the set     JavaSetAdaptor    Add a new element to the set     LinkedHashSet    Add a new element to the set     ListBuffer    Appends a single element to this buffer  It takes constant        Map    Add a key value pair to this map     Map    Add two or more key value pairs to this map     Map    This method defines syntactic sugar for adding or modifying        MapProxy    Add a key value pair to this map     MapProxy    Add two or more key value pairs to this map     ObservableSet    Add a new element to the set     PriorityQueue    Add two or more elements to this set     PriorityQueue    Inserts a single element into the priority queue     PriorityQueueProxy    Inserts a single element into the priority queue     Queue    Inserts a single element at the end of the queue     QueueProxy    Inserts a single element at the end of the queue     Set    Add a new element to the set     Set    Add two or more elements to this set     SetProxy    Add a new element to the set     Stack    Pushes a single element on top of the stack     StackProxy    Pushes a single element on top of the stack     SynchronizedBuffer    Append a single element to this buffer     SynchronizedMap    Add a key value pair to this map     SynchronizedMap    Add two or more key value pairs to this map     SynchronizedPriorityQueue    Inserts a single element into the priority queue     SynchronizedQueue    Inserts a single element at the end of the queue     SynchronizedSet    Add a new element to the set     SynchronizedStack    Pushes a single element on top of the stack     RichStringBuilder    Append a single element to this buffer     Reactions    Add a reaction     RefBuffer    Append a single element to this buffer     CachedFileStorage    adds a node  setting this dirty to true as a side effect    IndexedStorage    adds a node  setting this dirty to true as a side effect    SetStorage    adds a node  setting this dirty to true as a side effect - gt  Map MapTo - gt  Map MapTo -- List    Computes the difference between this list and the given list     -- Map    Remove a sequence of keys from this map -- Set    Remove all the elements provided by an iterator     -- SortedMap    Remove a sequence of keys from this map -- MutableIterable    Operator shortcut for removeAll  -- Set    Operator shortcut for removeAll  -- Map    Remove a sequence of keys from this map -- MapProxy    Remove a sequence of keys from this map -- Set    Remove all the elements provided by an iterator     --  Map    Remove a sequence of keys from this map --  MapProxy    Remove a sequence of keys from this map --  Set    Remove all the elements provided by an iterator     --  SetProxy    Remove all the elements provided by an iterator     --  SynchronizedMap    Remove a sequence of keys from this map --  SynchronizedSet    Remove all the elements provided by an iterator     - BigDecimal    Subtraction of BigDecimals - BigInt    Subtraction of BigInts - Byte - Char - Double - Enumeration SetXX    Remove a single element from a set  - Float - Int - List    Computes the difference between this list and the given object     - Long - Short - EmptyMap    Remove a key from this map - EmptySet    Remove a single element from a set  - HashMap    Remove a key from this map - HashSet    Remove a single element from a set  - IntMap    Remove a key from this map - ListMap Node    Creates a new mapping without the given key      - ListMap    This creates a new mapping without the given key      - ListSet Node    - can be used to remove a single element from     - ListSet    - can be used to remove a single element from     - LongMap    Remove a key from this map - Map    Remove a key from this map - Map    Remove two or more keys from this map - Map1    Remove a key from this map - Map2    Remove a key from this map - Map3    Remove a key from this map - Map4    Remove a key from this map - Set    Remove a single element from a set  - Set    Remove two or more elements from this set  - Set1    Remove a single element from a set  - Set2    Remove a single element from a set  - Set3    Remove a single element from a set  - Set4    Remove a single element from a set  - SortedMap    Remove a key from this map - SortedMap    Remove two or more keys from this map - TreeHashMap    Remove a key from this map - TreeMap    Remove a key from this map - TreeSet    Remove a single element from a set  - UnbalancedTreeMap Node    Remove a key from this map - UnbalancedTreeMap    Remove a key from this map - Map    Remove a key from this map - MutableIterable - Set - ListBuffer    Removes a single element from the buffer and return     - Map    Remove a key from this map - Map    Remove two or more keys from this map - MapProxy    Remove a key from this map - MapProxy    Remove two or more keys from this map - Set    Remove a new element from the set  - Set    Remove two or more elements from this set  -  Buffer    removes  quot a quot  from the collection  -  Collection    removes  quot a quot  from the collection  -  Map    Remove a key from this map  noop if key is not present  -  BitSet    Clears the i-th bit  -  Buffer    Removes a single element from this buffer  at its first occurrence      -  HashMap    Remove a key from this map  noop if key is not present  -  HashSet    Removes a single element from a set  -  ImmutableMapAdaptor    Remove a key from this map  noop if key is not present  -  ImmutableSetAdaptor    Removes a single element from a set  -  JavaMapAdaptor    Remove a key from this map  noop if key is not present  -  JavaSetAdaptor    Removes a single element from a set  -  LinkedHashMap    Remove a key from this map  noop if key is not present  -  LinkedHashSet    Removes a single element from a set  -  ListBuffer    Remove a single element from this buffer  It takes linear time     -  Map    Remove a key from this map  noop if key is not present  -  Map    Remove two or more keys from this map -  MapProxy    Remove a key from this map  noop if key is not present  -  MapProxy    Remove two or more keys from this map -  ObservableMap    Remove a key from this map  noop if key is not present  -  ObservableSet    Removes a single element from a set  -  OpenHashMap    Remove a key from this map  noop if key is not present  -  Set    Remove two or more elements from this set  -  Set    Removes a single element from a set  -  SetProxy    Removes a single element from a set  -  SynchronizedMap    Remove a key from this map  noop if key is not present  -  SynchronizedMap    Remove two or more keys from this map -  SynchronizedSet    Removes a single element from a set  -  Reactions    Remove the given reaction  -  CachedFileStorage    removes a tree  setting this dirty to true as a side effect -  IndexedStorage    removes a tree  setting this dirty to true as a side effect    BigInt    Returns a pair of two BigInts containing  this   that  and  this   that      Iterable    Similar to foldLeft but can be used as        IterableProxy    Similar to foldLeft but can be used as        Iterator    Similar to foldLeft but can be used as       BigDecimal    Division of BigDecimals   BigInt    Division of BigInts   Byte   Char   Double   Float   Int   Long   Short     Document     List    List    Document    Iterable    An alias for foldRight         IterableProxy    An alias for foldRight         Iterator    An alias for foldRight         Any    o    arg0 is the same as o equals arg0      AnyRef    o    arg0 is the same as if  o eq null  arg0 eq null else o equals arg0      Boolean    Byte    Char    Double    Float    Int    Long    Short   Actor    Receives the next message from this actor s mailbox    Channel    Receives the next message from this Channel    InputChannel    Receives the next message from this Channel    Parsers Parser    Returns a parser that optionally parses what this parser parses    Parsers Parser    Returns a parser that optionally parses what this parser parses    NodeSeq    Projection function  Similar to XPath  use this    quot foo quot     NodeSeq    projection function  Similar to XPath  use this     foo   BigInt    Bitwise exclusive-or of BigInts   Boolean   Byte   Char   Int   Long   Short    Parsers Parser    A parser combinator for partial function application    Parsers Parser    A parser combinator for partial function application    Parsers Parser    A parser combinator for function application    Parsers Parser    A parser combinator for function application    Parsers UnitParser    A parser combinator for function application     Parsers Parser   BigInt    Bitwise or of BigInts   Boolean   Byte   Char   Enumeration Set32    Equivalent to    for bit sets  Returns a set       Enumeration Set32    Equivalent to   for bit sets  Returns a set       Enumeration Set64    Equivalent to    for bit sets  Returns a set       Enumeration Set64    Equivalent to   for bit sets  Returns a set       Enumeration SetXX    Equivalent to    for bit sets  Returns a set       Enumeration SetXX    Equivalent to   for bit sets  Returns a set       Int   Long   Short   Parsers Parser    A parser combinator for alternative composition   Parsers Parser    A parser combinator for alternative composition   Parsers UnitParser    A parser combinator for alternative composition    Boolean     Parsers Parser     Parsers Parser    A parser combinator for alternative with longest match composition     Parsers Parser    A parser combinator for alternative with longest match composition     Parsers UnitParser    A parser combinator for alternative with longest match composition    Parsers Parser    A parser combinator for non-back-tracking sequential composition    Parsers Parser    A parser combinator for non-back-tracking sequential composition with a unit-parser    Parsers Parser    A parser combinator for non-back-tracking sequential composition    Parsers UnitParser    A parser combinator for non-back-tracking sequential composition with a unit-parser    Parsers UnitParser    A parser combinator for non-back-tracking sequential composition   gt  Parsers Parser    A parser combinator for sequential composition which keeps only the right result   BigInt    Returns the bitwise complement of this BigNum   Parsers OnceParser    A parser combinator for sequential composition   Parsers Parser    A parser combinator for sequential composition   Parsers   Parsers OnceParser    A parser combinator for sequential composition with a unit-parser   Parsers OnceParser    A parser combinator for sequential composition   Parsers Parser    A parser combinator for sequential composition with a unit-parser   Parsers Parser    A parser combinator for sequential composition   Parsers UnitOnceParser    A parser combinator for sequential composition with a unit-parser   Parsers UnitOnceParser    A parser combinator for sequential composition   Parsers UnitParser    A parser combinator for sequential composition with a unit-parser   Parsers UnitParser    A parser combinator for sequential composition unary   Boolean unary   Byte unary   Char unary   Double unary   Float unary   Int unary   Long unary   Short unary - BigDecimal    Returns a BigDecimal whose value is the negation of this BigDecimal unary - BigInt    Returns a BigInt whose value is the negation of this BigInt unary - Byte unary - Char unary - Double unary - Float unary - Int unary - Long unary - Short unary   Byte unary   Char unary   Int unary   Long unary   Short

User · Answer

One  good  IMO  difference between Scala and other languages is that it lets you name your methods with almost any character   What you enumerate is not  punctuation  but plain and simple methods  and as such their behavior vary from one object to the other  though there are some conventions    For example  check the Scaladoc documentation for List  and you ll see some of the methods you mentioned here   Some things to keep in mind    Most of the times the A operator equal B combination translates to A   A operator B  like in the     or     examples  Methods that end in   are right associative  this means that A    B is actually B    A     You ll find most answers by browsing the Scala documentation  Keeping a reference here would duplicate efforts  and it would fall behind quickly

User · Answer

Regarding    there is another Stackoverflow entry which covers the    case  In short  it is used to construct Lists by  consing  a head element and a tail list  It is both a class which represents a cons ed list and which can be used as an extractor  but most commonly it is a method on a list  As Pablo Fernandez points out  since it ends in a colon  it is right associative  meaning the receiver of the method call is to the right  and the argument to the left of the operator  That way you can elegantly express the consing as prepending a new head element to an existing list   val x   2    3    Nil     same result as List 2  3  val y   1    x            yields List 1  2  3    This is equivalent to  val x   Nil    3     2     successively prepend 3 and 2 to an empty list val y   x    1             then prepend 1   The use as extractor object is as follows   def extract l  List Int     l match      case Nil            gt   empty     case head    Nil    gt   exactly one element      head          case head    tail   gt   more than one element     extract Nil              yields  empty  extract List 1           yields  exactly one element  1   extract List 2  3        yields  more than one element    This looks like an operator here  but it is really just another  more readable  way of writing  def extract2 l  List Int     l match      case Nil              gt   empty     case    head  Nil     gt   exactly one element      head          case    head  tail    gt   more than one element      You can read more about extractors in this post

User · Answer

I consider a modern IDE to be critical for understanding large scala projects   Since these operators are also methods  in intellij idea I just control-click or control-b into the definitions     You can control-click right into a cons operator      and end up at the scala javadoc saying  Adds an element at the beginning of this list    In user-defined operators  this becomes even more critical  since they could be defined in hard-to-find implicits    your IDE knows where the implicit was defined

User · Answer

As an addition to brilliant answers of Daniel and 0    I have to say that Scala understands Unicode analogs for some of the symbols  so instead of   for  n  lt - 1 to 10  n   2 match     case 0   gt  println  even     case 1   gt  println  odd       one may write  for  n   1 to 10  n   2 match     case 0   println  even     case 1   println  odd

User · Answer

Just adding to the other excellent answers  Scala offers two often criticized symbolic operators      foldLeft  and     foldRight  operators  the first being right-associative  So the following three statements are the equivalent     1 to 100   foldLeft  0          1 to 100       0            0      1 to 100              As are these three     1 to 100   foldRight  0          1 to 100       0              1 to 100      0

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I divide the operators  for the purpose of teaching  into four categories    Keywords reserved symbols Automatically imported methods Common methods Syntactic sugars composition   It is fortunate  then  that most categories are represented in the question   - gt        Automatically imported method          Syntactic sugar          Syntactic sugar composition or common method  lt         Common method          Typo  though it s probably based on Keyword composition          Common method          Common method   The exact meaning of most of these methods depend on the class that is defining them  For example   lt   on Int means  less than or equal to    The first one  - gt   I ll give as example below     is probably the method defined on List  though it could be the object of the same name   and     is probably the method defined on various Buffer classes   So  let s see them   Keywords reserved symbols  There are some symbols in Scala that are special  Two of them are considered proper keywords  while others are just  reserved   They are      Keywords  lt -     Used on for-comprehensions  to separate pattern from generator   gt      Used for function types  function literals and import renaming     Reserved               Delimit expressions and parameters               Delimit type parameters               Delimit blocks               Method call and path separator               Comments               Used in type notations               Type ascription or context bounds  lt    gt    lt        Upper  lower and view bounds  lt    lt           Start token for various XML elements               Strings               Indicate symbols and characters               Annotations and variable binding on pattern matching               Denote constant or enable arbitrary identifiers               Parameter separator               Statement separator               vararg expansion               Many different meanings   These are all part of the language  and  as such  can be found in any text that properly describe the language  such as Scala Specification PDF  itself   The last one  the underscore  deserve a special description  because it is so widely used  and has so many different meanings  Here s a sample   import scala         Wild card -- all of Scala is imported import scala   Predef   gt            Exception  everything except Predef def f M              Higher kinded type parameter def f m  M           Existential type                      Anonymous function placeholder parameter m                    Eta expansion of method into method value m                    Partial function application     gt  5               Discarded parameter case     gt             Wild card pattern -- matches anything f xs                 Sequence xs is passed as multiple parameters to f ys  T   case Seq xs          Identifier xs is bound to the whole matched sequence   I probably forgot some other meaning  though   Automatically imported methods  So  if you did not find the symbol you are looking for in the list above  then it must be a method  or part of one  But  often  you ll see some symbol and the documentation for the class will not have that method  When this happens  either you are looking at a composition of one or more methods with something else  or the method has been imported into scope  or is available through an imported implicit conversion   These can still be found on ScalaDoc  you just have to know where to look for them  Or  failing that  look at the index  presently broken on 2 9 1  but available on nightly    Every Scala code has three automatic imports      Not necessarily in this order import  root  java lang            root  denotes an absolute path import  root  scala   import  root  scala Predef     The first two only make classes and singleton objects available  The third one contains all implicit conversions and imported methods  since Predef is an object itself   Looking inside Predef quickly show some symbols   class  lt   lt  class     object  lt   lt  object       Any other symbol will be made available through an implicit conversion  Just look at the methods tagged with implicit that receive  as parameter  an object of type that is receiving the method  For example    a  - gt  1     Look for an implicit from String  AnyRef  Any or type parameter   In the above case  - gt  is defined in the class ArrowAssoc through the method any2ArrowAssoc that takes an object of type A  where A is an unbounded type parameter to the same method   Common methods  So  many symbols are simply methods on a class  For instance  if you do  List 1  2     List 3  4    You ll find the method    right on the ScalaDoc for List  However  there s one convention that you must be aware when searching for methods  Methods ending in colon     bind to the right instead of the left  In other words  while the above method call is equivalent to   List 1  2     List 3  4     If I had  instead 1    List 2  3   that would be equivalent to   List 2  3     1    So you need to look at the type found on the right when looking for methods ending in colon  Consider  for instance   1    List 2  3     4   The first method      binds to the right  and is found on List  The second method      is just a normal method  and binds to the left -- again  on List   Syntactic sugars composition  So  here s a few syntactic sugars that may hide a method   class Example arr  Array Int    Array fill 5  0       def apply n  Int    arr n    def update n  Int  v  Int    arr n    v   def a   arr 0   def a   v  Int    arr 0    v   def b   arr 1   def b   v  Int    arr 1    v   def c   arr 2   def c   v  Int    arr 2    v   def d   arr 3   def d   v  Int    arr 3    v   def e   arr 4   def e   v  Int    arr 4    v   def   v  Int    new Example arr map      v     def unapply n  Int    if  arr indices contains n  Some arr n   else None    val Ex   new Example    or var for the last example println Ex 0       calls apply 0  Ex 0    2          calls update 0  2  Ex b   3           calls b   3     This requires Ex to be a  val  val Ex c    2      calls unapply 2  and assigns result to c    This requires Ex to be a  var  Ex    1            substituted for Ex   Ex   1   The last one is interesting  because any symbolic method can be combined to form an assignment-like method that way   And  of course  there s various combinations that can appear in code            An expression  or parameter  that is an anonymous function with          two parameters  used exactly where the underscores appear  and          which calls the     method on the first parameter passing the          second parameter as argument

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Scala inherits most of Java s arithmetic operators  This includes bitwise-or    single pipe character   bitwise-and  amp   bitwise-exclusive-or    as well as logical  boolean  or     two pipe characters  and logical-and  amp  amp   Interestingly  you can use the single character operators on boolean  so the java ish logical operators are totally redundant   true  amp  amp  true      valid true  amp  true       valid as well  3  amp  4             bitwise-and  011  amp  100 yields 000  3  amp  amp  4            not valid   As pointed out in another post  calls ending in an equals sign    are resolved  if a method with that name does not exist   by a reassignment   var x   3 x    1                 is not a method in  int   Scala makes it  x   x   1    This  double-check  makes it possible  to easily exchange a mutable for an immutable collection   val m   collection mutable Set  Hallo         m  a val  but holds mutable coll var i   collection immutable Set  Hallo       i  is a var  but holds immutable coll  m     Welt     destructive call m     Welt   i     Welt     re-assignment i   i    Welt   creates a new immutable Set

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You can group those first according to some criteria  In this post I will just explain the underscore character and the right-arrow       contains a period  A period in Scala always indicates a method call  So left of the period you have the receiver  and right of it the message  method name   Now   is a special symbol in Scala  There are several posts about it  for example this blog entry all use cases  Here it is an anonymous function short cut  that is it a shortcut for a function that takes one argument and invokes the method   on it  Now   is not a valid method  so most certainly you were seeing    1 or something similar  that is  invoking method    1 on the function argument   1 to  22 are the methods of tuples which extract a particular element of a tuple  Example   val tup     Hallo   33  tup  1    extracts  Hallo  tup  2    extracts 33   Now lets assume a use case for the function application shortcut  Given a map which maps integers to strings   val coll   Map 1 - gt   Eins   2 - gt   Zwei   3 - gt   Drei     Wooop  there is already another occurrence of a strange punctuation  The hyphen and greater-than characters  which resemble a right-hand arrow  is an operator which produces a Tuple2  So there is no difference in the outcome of writing either  1   Eins   or 1 - gt   Eins   only that the latter is easier to read  especially in a list of tuples like the map example  The - gt  is no magic  it is  like a few other operators  available because you have all implicit conversions in object scala Predef in scope  The conversion which takes place here is  implicit def any2ArrowAssoc  A   x  A   ArrowAssoc A     Where ArrowAssoc has the - gt  method which creates the Tuple2  Thus 1 - gt   Eins  is actual the call Predef any2ArrowAssoc 1  - gt   Eins    Ok  Now back to the original question with the underscore character      lets create a sequence from the map by returning the    values in reverse  coll map    2 reverse     yields List sniE  iewZ  ierD    The underscore here shortens the following equivalent code   coll map tup   gt  tup  2 reverse    Note that the map method of a Map passes in the tuple of key and value to the function argument  Since we are only interested in the values  the strings   we extract them with the  2 method on the tuple

[scala] What do all of Scala's symbolic operators mean?

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