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Diffstat (limited to 'doc/syntax/literals.rdoc')
| -rw-r--r-- | doc/syntax/literals.rdoc | 206 |
1 files changed, 152 insertions, 54 deletions
diff --git a/doc/syntax/literals.rdoc b/doc/syntax/literals.rdoc index 0c1e4a434b..c876558d4e 100644 --- a/doc/syntax/literals.rdoc +++ b/doc/syntax/literals.rdoc @@ -3,7 +3,7 @@ Literals create objects you can use in your program. Literals include: * {Boolean and Nil Literals}[#label-Boolean+and+Nil+Literals] -* {Number Literals}[#label-Number+Literals] +* {Numeric Literals}[#label-Numeric+Literals] * {Integer Literals}[#label-Integer+Literals] * {Float Literals}[#label-Float+Literals] @@ -36,7 +36,7 @@ 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. -== Number Literals +== \Numeric Literals === \Integer Literals @@ -136,9 +136,9 @@ Also \Rational numbers may be imaginary numbers. 12.3ir #=> Syntax error -== Strings +== \String Literals -=== \String Literals +=== Double-Quoted \String Literals The most common way of writing strings is using <tt>"</tt>: @@ -150,35 +150,14 @@ Any internal <tt>"</tt> must be escaped: "This string has a quote: \". As you can see, it is escaped" -Double-quote strings allow escaped characters such as <tt>\n</tt> for -newline, <tt>\t</tt> for tab, etc. The full list of supported escape -sequences are as follows: - - \a bell, ASCII 07h (BEL) - \b backspace, ASCII 08h (BS) - \t horizontal tab, ASCII 09h (TAB) - \n newline (line feed), ASCII 0Ah (LF) - \v vertical tab, ASCII 0Bh (VT) - \f form feed, ASCII 0Ch (FF) - \r carriage return, ASCII 0Dh (CR) - \e escape, ASCII 1Bh (ESC) - \s space, ASCII 20h (SPC) - \\ backslash, \ - \nnn octal bit pattern, where nnn is 1-3 octal digits ([0-7]) - \xnn hexadecimal bit pattern, where nn is 1-2 hexadecimal digits ([0-9a-fA-F]) - \unnnn Unicode character, where nnnn is exactly 4 hexadecimal digits ([0-9a-fA-F]) - \u{nnnn ...} Unicode character(s), where each nnnn is 1-6 hexadecimal digits ([0-9a-fA-F]) - \cx or \C-x control character, where x is an ASCII printable character - \M-x meta character, where x is an ASCII printable character - \M-\C-x meta control character, where x is an ASCII printable character - \M-\cx same as above - \c\M-x same as above - \c? or \C-? delete, ASCII 7Fh (DEL) +Double-quoted strings allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. -Any other character following a backslash is interpreted as the +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}" @@ -190,8 +169,14 @@ 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}" @@ -199,6 +184,16 @@ In addition to disabling interpolation, single-quoted strings also disable all escape sequences except for the single-quote (<tt>\'</tt>) and backslash (<tt>\\\\</tt>). +In a single-quoted string, +any other character following a backslash is interpreted as is: +a backslash and the character itself. + +See also: + +* {%q: Non-Interpolable String Literals}[#label-25q-3A+Non-Interpolable+String+Literals] + +=== Literal String Concatenation + Adjacent string literals are automatically concatenated by the interpreter: "con" "cat" "en" "at" "ion" #=> "concatenation" @@ -209,12 +204,14 @@ Any combination of adjacent single-quote, double-quote, percent strings will be concatenated as long as a percent-string is not last. %q{a} 'b' "c" #=> "abc" - "a" 'b' %q{c} #=> NameError: uninitialized constant q + "a" 'b' %q{c} #=> NoMethodError: undefined method 'q' for main + +=== 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 @@ -228,10 +225,45 @@ a single codepoint in the script encoding: ?\C-\M-a #=> "\x81", same as above ?あ #=> "あ" -See also: +=== Escape Sequences -* {%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] +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>). + +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: + + \a bell, ASCII 07h (BEL) + \b backspace, ASCII 08h (BS) + \t horizontal tab, ASCII 09h (TAB) + \n newline (line feed), ASCII 0Ah (LF) + \v vertical tab, ASCII 0Bh (VT) + \f form feed, ASCII 0Ch (FF) + \r carriage return, ASCII 0Dh (CR) + \e escape, ASCII 1Bh (ESC) + \s space, ASCII 20h (SPC) + \\ backslash, \ + \nnn octal bit pattern, where nnn is 1-3 octal digits ([0-7]) + \xnn hexadecimal bit pattern, where nn is 1-2 hexadecimal digits ([0-9a-fA-F]) + \unnnn Unicode character, where nnnn is exactly 4 hexadecimal digits ([0-9a-fA-F]) + \u{nnnn ...} Unicode character(s), where each nnnn is 1-6 hexadecimal digits ([0-9a-fA-F]) + \cx or \C-x control character, where x is an ASCII printable character + \M-x meta character, where x is an ASCII printable character + \M-\C-x meta control character, where x is an ASCII printable character + \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. === Here Document Literals @@ -283,9 +315,10 @@ 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 escaped characters. You may disable -interpolation and escaping by surrounding the opening identifier with single -quotes: +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} @@ -326,12 +359,15 @@ 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}" @@ -451,7 +487,12 @@ may use these paired delimiters: * <tt>(</tt> and <tt>)</tt>. * <tt>{</tt> and <tt>}</tt>. * <tt><</tt> and <tt>></tt>. -* Any other character, as both beginning and ending delimiters. +* 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. @@ -460,13 +501,20 @@ These are demonstrated in the next section. 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: - %[foo bar baz] # => "foo bar baz" # Using []. - %(foo bar baz) # => "foo bar baz" # Using (). - %{foo bar baz} # => "foo bar baz" # Using {}. - %<foo bar baz> # => "foo bar baz" # Using <>. - %|foo bar baz| # => "foo bar baz" # Using two |. - %:foo bar baz: # => "foo bar baz" # Using two :. + %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 backslashes and +the specified delimiters can be escaped with a backslash. === <tt>% and %Q</tt>: Interpolable String Literals @@ -476,30 +524,70 @@ 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 with <tt>%w</tt> (non-interpolable) -or <tt>%W</tt> (interpolable): +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 interpolated string is treated as a single word even if it contains +whitespace. + + s = "bar baz" + %W[foo #{s} zot] #=> ["foo", "bar baz", "zot"] + %W[foo #{"bar baz zot"} qux] # => ["foo", "bar baz zot", "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 with <tt>%i</tt> (non-interpolable) -or <tt>%I</tt> (interpolable): +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>: @@ -507,6 +595,10 @@ 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 backslashes 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>; @@ -531,4 +623,10 @@ See {Regexp modes}[rdoc-ref:Regexp@Modes] for details. You can write and execute a shell command with <tt>%x</tt>: - %x(echo 1) # => "1\n" + %x(echo 1) # => "1\n" + %x[echo #{1 + 2}] # => "3\n" + %x[echo \u0030] # => "0\n" + +This is interpolable. +<tt>%x</tt> allow escape sequences described in +{Escape Sequences}[#label-Escape+Sequences]. |