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Diffstat (limited to 'doc/syntax/literals.rdoc')
| -rw-r--r-- | doc/syntax/literals.rdoc | 404 |
1 files changed, 314 insertions, 90 deletions
diff --git a/doc/syntax/literals.rdoc b/doc/syntax/literals.rdoc index cfdbb71700..6d681419a2 100644 --- a/doc/syntax/literals.rdoc +++ b/doc/syntax/literals.rdoc @@ -2,17 +2,33 @@ Literals create objects you can use in your program. Literals include: -* Booleans and nil -* Numbers -* Strings -* Symbols -* Arrays -* Hashes -* Ranges -* Regular Expressions -* Procs - -== Booleans and nil +* {Boolean and Nil Literals}[#label-Boolean+and+Nil+Literals] +* {Number Literals}[#label-Number+Literals] + + * {Integer Literals}[#label-Integer+Literals] + * {Float Literals}[#label-Float+Literals] + * {Rational Literals}[#label-Rational+Literals] + * {Complex Literals}[#label-Complex+Literals] + +* {String Literals}[#label-String+Literals] +* {Here Document Literals}[#label-Here+Document+Literals] +* {Symbol Literals}[#label-Symbol+Literals] +* {Array Literals}[#label-Array+Literals] +* {Hash Literals}[#label-Hash+Literals] +* {Range Literals}[#label-Range+Literals] +* {Regexp Literals}[#label-Regexp+Literals] +* {Lambda Proc Literals}[#label-Lambda+Proc+Literals] +* {Percent Literals}[#label-Percent+Literals] + + * {%q: Non-Interpolable String Literals}[#label-25q-3A+Non-Interpolable+String+Literals] + * {% and %Q: Interpolable String Literals}[#label-25+and+-25Q-3A+Interpolable+String+Literals] + * {%w and %W: String-Array Literals}[#label-25w+and+-25W-3A+String-Array+Literals] + * {%i and %I: Symbol-Array Literals}[#label-25i+and+-25I-3A+Symbol-Array+Literals] + * {%r: Regexp Literals}[#label-25r-3A+Regexp+Literals] + * {%s: Symbol Literals}[#label-25s-3A+Symbol+Literals] + * {%x: Backtick Literals}[#label-25x-3A+Backtick+Literals] + +== Boolean and Nil Literals +nil+ and +false+ are both false values. +nil+ is sometimes used to indicate "no value" or "unknown" but evaluates to +false+ in conditional expressions. @@ -20,7 +36,9 @@ Literals create objects you can use in your program. Literals include: +true+ is a true value. All objects except +nil+ and +false+ evaluate to a true value in conditional expressions. -== Numbers +== Number Literals + +=== \Integer Literals You can write integers of any size as follows: @@ -31,15 +49,6 @@ These numbers have the same value, 1,234. The underscore may be used to enhance readability for humans. You may place an underscore anywhere in the number. -Floating point numbers may be written as follows: - - 12.34 - 1234e-2 - 1.234E1 - -These numbers have the same value, 12.34. You may use underscores in floating -point numbers as well. - You can use a special prefix to write numbers in decimal, hexadecimal, octal or binary formats. For decimal numbers use a prefix of <tt>0d</tt>, for hexadecimal numbers use a prefix of <tt>0x</tt>, for octal numbers use a @@ -68,46 +77,79 @@ Examples: All these numbers have the same decimal value, 170. Like integers and floats you may use an underscore for readability. -=== Rational numbers +=== \Float Literals -Numbers suffixed by +r+ are Rational numbers. +Floating-point numbers may be written as follows: - 12r #=> (12/1) - 12.3r #=> (123/10) + 12.34 + 1234e-2 + 1.234E1 -Rational numbers are exact, whereas Float numbers are inexact. +These numbers have the same value, 12.34. You may use underscores in floating +point numbers as well. + +=== \Rational Literals + +You can write a Rational literal using a special suffix, <tt>'r'</tt>. + +Examples: - 0.1r + 0.2r #=> (3/10) - 0.1 + 0.2 #=> 0.30000000000000004 + 1r # => (1/1) + 2/3r # => (2/3) # With denominator. + -1r # => (-1/1) # With signs. + -2/3r # => (-2/3) + 2/-3r # => (-2/3) + -2/-3r # => (2/3) + +1/+3r # => (1/3) + 1.2r # => (6/5) # With fractional part. + 1_1/2_1r # => (11/21) # With embedded underscores. + 2/4r # => (1/2) # Automatically reduced. -=== Complex numbers +Syntax: -Numbers suffixed by +i+ are Complex (or imaginary) numbers. + <rational-literal> = <numerator> [ '/' <denominator> ] 'r' + <numerator> = [ <sign> ] <digits> [ <fractional-part> ] + <fractional-part> = '.' <digits> + <denominator> = [ sign ] <digits> + <sign> = '-' | '+' + <digits> = <digit> { <digit> | '_' <digit> } + <digit> = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' + +Note this, which is parsed as \Float numerator <tt>1.2</tt> +divided by \Rational denominator <tt>3r</tt>, +resulting in a \Float: + + 1.2/3r # => 0.39999999999999997 + +=== \Complex Literals + +You can write a Complex number as follows (suffixed +i+): 1i #=> (0+1i) 1i * 1i #=> (-1+0i) -Also Rational numbers may be imaginary numbers. +Also \Rational numbers may be imaginary numbers. 12.3ri #=> (0+(123/10)*i) -+i+ must be placed after +r+, the opposite is not allowed. ++i+ must be placed after +r+; the opposite is not allowed. - 12.3ir #=> syntax error + 12.3ir #=> Syntax error == Strings -The most common way of writing strings is using <tt>"</tt>: - - "This is a string." - -The string may be many lines long. - -Any internal <tt>"</tt> must be escaped: +=== Escape Sequences - "This string has a quote: \". As you can see, it is escaped" +Some characters can be represented as escape sequences in +double-quoted strings, +character literals, +here document literals (non-quoted, double-quoted, and with backticks), +double-quoted symbols, +double-quoted symbol keys in Hash literals, +Regexp literals, and +several percent literals (<tt>%</tt>, <tt>%Q,</tt> <tt>%W</tt>, <tt>%I</tt>, <tt>%r</tt>, <tt>%x</tt>). -Double-quote strings allow escaped characters such as <tt>\n</tt> for +They allow escape sequences such as <tt>\n</tt> for newline, <tt>\t</tt> for tab, etc. The full list of supported escape sequences are as follows: @@ -131,11 +173,31 @@ sequences are as follows: \M-\cx same as above \c\M-x same as above \c? or \C-? delete, ASCII 7Fh (DEL) + \<newline> continuation line (empty string) + +The last one, <tt>\<newline></tt>, represents an empty string instead of a character. +It is used to fold a line in a string. + +=== Double-quoted \String Literals -Any other character following a backslash is interpreted as the +The most common way of writing strings is using <tt>"</tt>: + + "This is a string." + +The string may be many lines long. + +Any internal <tt>"</tt> must be escaped: + + "This string has a quote: \". As you can see, it is escaped" + +Double-quoted strings allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. + +In a double-quoted string, +any other character following a backslash is interpreted as the character itself. -Double-quote strings allow interpolation of other values using +Double-quoted strings allow interpolation of other values using <tt>#{...}</tt>: "One plus one is two: #{1 + 1}" @@ -147,8 +209,14 @@ You can also use <tt>#@foo</tt>, <tt>#@@foo</tt> and <tt>#$foo</tt> as a shorthand for, respectively, <tt>#{ @foo }</tt>, <tt>#{ @@foo }</tt> and <tt>#{ $foo }</tt>. +See also: + +* {% and %Q: Interpolable String Literals}[#label-25+and+-25Q-3A+Interpolable+String+Literals] + +=== Single-quoted \String Literals + Interpolation may be disabled by escaping the "#" character or using -single-quote strings: +single-quoted strings: '#{1 + 1}' #=> "\#{1 + 1}" @@ -156,14 +224,15 @@ In addition to disabling interpolation, single-quoted strings also disable all escape sequences except for the single-quote (<tt>\'</tt>) and backslash (<tt>\\\\</tt>). -You may also create strings using <tt>%</tt>: +In a single-quoted string, +any other character following a backslash is interpreted as is: +a backslash and the character itself. - %(1 + 1 is #{1 + 1}) #=> "1 + 1 is 2" +See also: -There are two different types of <tt>%</tt> strings <tt>%q(...)</tt> behaves -like a single-quote string (no interpolation or character escaping), while -<tt>%Q</tt> behaves as a double-quote string. See Percent Strings below for -more discussion of the syntax of percent strings. +* {%q: Non-Interpolable String Literals}[#label-25q-3A+Non-Interpolable+String+Literals] + +=== Literal String Concatenation Adjacent string literals are automatically concatenated by the interpreter: @@ -177,10 +246,12 @@ be concatenated as long as a percent-string is not last. %q{a} 'b' "c" #=> "abc" "a" 'b' %q{c} #=> NameError: uninitialized constant q +=== Character Literal + There is also a character literal notation to represent single character strings, which syntax is a question mark (<tt>?</tt>) -followed by a single character or escape sequence that corresponds to -a single codepoint in the script encoding: +followed by a single character or escape sequence (except continuation line) +that corresponds to a single codepoint in the script encoding: ?a #=> "a" ?abc #=> SyntaxError @@ -194,7 +265,7 @@ a single codepoint in the script encoding: ?\C-\M-a #=> "\x81", same as above ?あ #=> "あ" -=== Here Documents (heredocs) +=== Here Document Literals If you are writing a large block of text you may use a "here document" or "heredoc": @@ -238,9 +309,16 @@ the content. Note that empty lines and lines consisting solely of literal tabs and spaces will be ignored for the purposes of determining indentation, but escaped tabs and spaces are considered non-indentation characters. -A heredoc allows interpolation and escaped characters. You may disable -interpolation and escaping by surrounding the opening identifier with single -quotes: +For the purpose of measuring an indentation, a horizontal tab is regarded as a +sequence of one to eight spaces such that the column position corresponding to +its end is a multiple of eight. The amount to be removed is counted in terms +of the number of spaces. If the boundary appears in the middle of a tab, that +tab is not removed. + +A heredoc allows interpolation and the escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. +You may disable interpolation and the escaping by surrounding the opening +identifier with single quotes: expected_result = <<-'EXPECTED' One plus one is #{1 + 1} @@ -274,26 +352,34 @@ read: content for heredoc two TWO -== Symbols +== \Symbol Literals A Symbol represents a name inside the ruby interpreter. See Symbol for more details on what symbols are and when ruby creates them internally. You may reference a symbol using a colon: <tt>:my_symbol</tt>. -You may also create symbols by interpolation: +You may also create symbols by interpolation and escape sequences described in +{Escape Sequences}[#label-Escape+Sequences] with double-quotes: :"my_symbol1" :"my_symbol#{1 + 1}" + :"foo\sbar" -Like strings, a single-quote may be used to disable interpolation: +Like strings, a single-quote may be used to disable interpolation and +escape sequences: :'my_symbol#{1 + 1}' #=> :"my_symbol\#{1 + 1}" When creating a Hash, there is a special syntax for referencing a Symbol as well. -== Arrays +See also: + +* {%s: Symbol Literals}[#label-25s-3A+Symbol+Literals] + + +== \Array Literals An array is created using the objects between <tt>[</tt> and <tt>]</tt>: @@ -304,9 +390,14 @@ You may place expressions inside the array: [1, 1 + 1, 1 + 2] [1, [1 + 1, [1 + 2]]] +See also: + +* {%w and %W: String-Array Literals}[#label-25w+and+-25W-3A+String-Array+Literals] +* {%i and %I: Symbol-Array Literals}[#label-25i+and+-25I-3A+Symbol-Array+Literals] + See Array for the methods you may use with an array. -== Hashes +== \Hash Literals A hash is created using key-value pairs between <tt>{</tt> and <tt>}</tt>: @@ -328,9 +419,17 @@ is equal to { :"a 1" => 1, :"b 2" => 2 } +Hash values can be omitted, meaning that value will be fetched from the context +by the name of the key: + + x = 100 + y = 200 + h = { x:, y: } + #=> {:x=>100, :y=>200} + See Hash for the methods you may use with a hash. -== Ranges +== \Range Literals A range represents an interval of values. The range may include or exclude its ending value. @@ -343,25 +442,29 @@ its ending value. You may create a range of any object. See the Range documentation for details on the methods you need to implement. -== Regular Expressions - -A regular expression is created using "/": +== \Regexp Literals - /my regular expression/ +A regular expression may be created using leading and trailing +slash (<tt>'/'</tt>) characters: -The regular expression may be followed by flags which adjust the matching -behavior of the regular expression. The "i" flag makes the regular expression -case-insensitive: + re = /foo/ # => /foo/ + re.class # => Regexp - /my regular expression/i +The trailing slash may be followed by one or more modifiers characters +that set modes for the regexp. +See {Regexp modes}[rdoc-ref:Regexp@Modes] for details. Interpolation may be used inside regular expressions along with escaped characters. Note that a regular expression may require additional escaped characters than a string. +See also: + +* {%r: Regexp Literals}[#label-25r-3A+Regexp+Literals] + See Regexp for a description of the syntax of regular expressions. -== Procs +== Lambda Proc Literals A lambda proc can be created with <tt>-></tt>: @@ -375,27 +478,148 @@ You can require arguments for the proc as follows: This proc will add one to its argument. -== Percent Strings +== Percent Literals + +Each of the literals in described in this section +may use these paired delimiters: + +* <tt>[</tt> and <tt>]</tt>. +* <tt>(</tt> and <tt>)</tt>. +* <tt>{</tt> and <tt>}</tt>. +* <tt><</tt> and <tt>></tt>. +* Non-alphanumeric ASCII character except above, as both beginning and ending delimiters. + +The delimiters can be escaped with a backslash. +However, the first four pairs (brackets, parenthesis, braces, and +angle brackets) are allowed without backslash as far as they are correctly +paired. + +These are demonstrated in the next section. + +=== <tt>%q</tt>: Non-Interpolable String Literals + +You can write a non-interpolable string with <tt>%q</tt>. +The created string is the same as if you created it with single quotes: + + %q[foo bar baz] # => "foo bar baz" # Using []. + %q(foo bar baz) # => "foo bar baz" # Using (). + %q{foo bar baz} # => "foo bar baz" # Using {}. + %q<foo bar baz> # => "foo bar baz" # Using <>. + %q|foo bar baz| # => "foo bar baz" # Using two |. + %q:foo bar baz: # => "foo bar baz" # Using two :. + %q(1 + 1 is #{1 + 1}) # => "1 + 1 is \#{1 + 1}" # No interpolation. + %q[foo[bar]baz] # => "foo[bar]baz" # brackets can be nested. + %q(foo(bar)baz) # => "foo(bar)baz" # parenthesis can be nested. + %q{foo{bar}baz} # => "foo{bar}baz" # braces can be nested. + %q<foo<bar>baz> # => "foo<bar>baz" # angle brackets can be nested. + +This is similar to single-quoted string but only backslashs and +the specified delimiters can be escaped with a backslash. + +=== <tt>% and %Q</tt>: Interpolable String Literals + +You can write an interpolable string with <tt>%Q</tt> +or with its alias <tt>%</tt>: + + %[foo bar baz] # => "foo bar baz" + %(1 + 1 is #{1 + 1}) # => "1 + 1 is 2" # Interpolation. + +This is similar to double-quoted string. +It allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. +Other escaped characters (a backslash followed by a character) are +interpreted as the character. + +=== <tt>%w and %W</tt>: String-Array Literals + +You can write an array of strings as whitespace-separated words +with <tt>%w</tt> (non-interpolable) or <tt>%W</tt> (interpolable): + + %w[foo bar baz] # => ["foo", "bar", "baz"] + %w[1 % *] # => ["1", "%", "*"] + # Use backslash to embed spaces in the strings. + %w[foo\ bar baz\ bat] # => ["foo bar", "baz bat"] + %W[foo\ bar baz\ bat] # => ["foo bar", "baz bat"] + %w(#{1 + 1}) # => ["\#{1", "+", "1}"] + %W(#{1 + 1}) # => ["2"] + + # The nested delimiters evaluated to a flat array of strings + # (not nested array). + %w[foo[bar baz]qux] # => ["foo[bar", "baz]qux"] + +The following characters are considered as white spaces to separate words: + +* space, ASCII 20h (SPC) +* form feed, ASCII 0Ch (FF) +* newline (line feed), ASCII 0Ah (LF) +* carriage return, ASCII 0Dh (CR) +* horizontal tab, ASCII 09h (TAB) +* vertical tab, ASCII 0Bh (VT) + +The white space characters can be escaped with a backslash to make them +part of a word. + +<tt>%W</tt> allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. +However the continuation line <tt>\<newline></tt> is not usable because +it is interpreted as the escaped newline described above. + +=== <tt>%i and %I</tt>: Symbol-Array Literals + +You can write an array of symbols as whitespace-separated words +with <tt>%i</tt> (non-interpolable) or <tt>%I</tt> (interpolable): + + %i[foo bar baz] # => [:foo, :bar, :baz] + %i[1 % *] # => [:"1", :%, :*] + # Use backslash to embed spaces in the symbols. + %i[foo\ bar baz\ bat] # => [:"foo bar", :"baz bat"] + %I[foo\ bar baz\ bat] # => [:"foo bar", :"baz bat"] + %i(#{1 + 1}) # => [:"\#{1", :+, :"1}"] + %I(#{1 + 1}) # => [:"2"] + +The white space characters and its escapes are interpreted as the same as +string-array literals described in +{%w and %W: String-Array Literals}[#label-25w+and+-25W-3A+String-Array+Literals]. + +=== <tt>%s</tt>: Symbol Literals + +You can write a symbol with <tt>%s</tt>: + + %s[foo] # => :foo + %s[foo bar] # => :"foo bar" + +This is non-interpolable. +No interpolation allowed. +Only backslashs and the specified delimiters can be escaped with a backslash. + +=== <tt>%r</tt>: Regexp Literals + +You can write a regular expression with <tt>%r</tt>; +the character used as the leading and trailing delimiter +may be (almost) any character: + + %r/foo/ # => /foo/ + %r:name/value pair: # => /name\/value pair/ + +A few "symmetrical" character pairs may be used as delimiters: -Besides <tt>%(...)</tt> which creates a String, the <tt>%</tt> may create -other types of object. As with strings, an uppercase letter allows -interpolation and escaped characters while a lowercase letter disables them. + %r[foo] # => /foo/ + %r{foo} # => /foo/ + %r(foo) # => /foo/ + %r<foo> # => /foo/ -These are the types of percent strings in ruby: +The trailing delimiter may be followed by one or more modifier characters +that set modes for the regexp. +See {Regexp modes}[rdoc-ref:Regexp@Modes] for details. -<tt>%i</tt> :: Array of Symbols -<tt>%q</tt> :: String -<tt>%r</tt> :: Regular Expression -<tt>%s</tt> :: Symbol -<tt>%w</tt> :: Array of Strings -<tt>%x</tt> :: Backtick (capture subshell result) +=== <tt>%x</tt>: Backtick Literals -For the two array forms of percent string, if you wish to include a space in -one of the array entries you must escape it with a "\\" character: +You can write and execute a shell command with <tt>%x</tt>: - %w[one one-hundred\ one] - #=> ["one", "one-hundred one"] + %x(echo 1) # => "1\n" + %x[echo #{1 + 2}] # => "3\n" + %x[echo \u0030] # => "0\n" -If you are using "(", "[", "{", "<" you must close it with ")", "]", "}", ">" -respectively. You may use most other non-alphanumeric characters for percent -string delimiters such as "%", "|", "^", etc. +This is interpolable. +<tt>%x</tt> allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. |