Ruby變量
2010-07-09 星期五 小雨 ruby與大部分腳本語言不同,它有自己的命名規則(采用CoC): 1. 常量(Constants) :首字母必須大寫(一般是整個單詞都是大寫的) A variable whose name begins with an uppercase letter (A-Z) is a constant. A constant can be reassigned a value after its initialization, but doing so will generate a warning. Every class is a constant.(因為/是以在ruby中,類名都是首字母大寫的) Trying to substitute the value of a constant or trying to access an uninitialized constant raises the NameError exception.
例子:FOOBAR 2. 局部變量(Local Variables) 與強類型語言(如C、C++、Java一樣): A variable whose name begins with a lowercase letter (a-z) or underscore (_) is a local variable or method invocation. The scope of a local variable ranges from class, module, def, or do to the corresponding end or from a block's opening brace to its close brace {}. A local variable is only accessible from within the block of its initialization. For example:
i0 = 1
loop {
i1 = 2
puts defined?(i0) # true; "i0" was initialized in the ascendant block
puts defined?(i1) # true; "i1" was initialized in this block
break
}
puts defined?(i0) # true; "i0 was initialized in this block
puts defined?(i1) # false; "i1" was initialized in the loop
與腳本語言不同(如perl),不需要前面加$符号,也不需要my關鍵詞。 3. 執行個體變量(Instance Variables) A variable whose name begins with '@' is an instance variable of self. An instance variable belongs to the object itself. Uninitialized instance variables have a value of nil. 例如:@foobar
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4. 類變量(Class Variables) A class variable is shared by all instances of a class. 其實就是類靜态變量 例子: @@foobar
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Here @@no_of_customers is a class variable. This will produce following result:
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5. 全局變量(Global Variables) A variable whose name begins with '$' has a global scope; meaning it can be accessed from anywhere within the program during runtime. 例子:$foobar
6. 僞變量(Pseudo Variables)
self
- Execution context of the current method.
nil
- The sole-instance of the
class. Expresses nothing.NilClass
true
- The sole-instance of the
class. Expresses true.TrueClass
false
- The sole-instance of the
class. Expresses false. ( nil also is considered to be false, and every other value is considered to be true in Ruby.)FalseClass
The value of a pseudo variable cannot be changed. Substitution to a pseudo variable causes an exception to be raised.
7. 預定義變量(Pre-defined Variables)
$! The exception information message set by the last 'raise' (last exception thrown).
[email protected] Array of the backtrace of the last exception thrown.
$& The string matched by the last successful pattern match in this scope.
$` The string to the left of the last successful match.
$' The string to the right of the last successful match.
$+ The last bracket matched by the last successful match.
$1 to $9 The Nth group of the last successful regexp match.
$~ The information about the last match in the current scope.
$= The flag for case insensitive, nil by default (deprecated).
$/ The input record separator, newline by default.
$/ The output record separator for the print and IO#write. Default is nil.
$, The output field separator for the print and Array#join.
$; The default separator for String#split.
$. The current input line number of the last file that was read.
$< The virtual concatenation file of the files given on command line.
$> The default output for print, printf. $stdout by default.
$_ The last input line of string by gets or readline.
$0 Contains the name of the script being executed. May be assignable.
$* Command line arguments given for the script. Same as ARGV.
$$ The process number of the Ruby running this script. Same as Process.pid.
$? The status of the last executed child process.
$: Load path for scripts and binary modules by load or require.
$" The array contains the module names loaded by require.
$LOADED_FEATURES An english friendlier alias to $"
$DEBUG The status of the -d switch. Assignable.
$FILENAME Current input file from $<. Same as $<.filename.
$KCODE Character encoding of the source code.
$LOAD_PATH An alias to $:
$stderr The current standard error output.
$stdin The current standard input.
$stdout The current standard output.
$VERBOSE The verbose flag, which is set by the -v switch.
$-0 The alias to $/
$-a True if option -a ("autosplit" mode) is set. Read-only variable.
$-d The alias to $DEBUG.
$-F The alias to $;
$-i If in-place-edit mode is set, this variable holds the extension, otherwise nil.
$-I The alias to $:
$-K The alias to $KCODE.
$-l True if option -l is set ("line-ending processing" is on). Read-only variable.
$-p True if option -p is set ("loop" mode is on). Read-only variable.
$-v The alias to $VERBOSE.
$-w True if option -w is set.
This infestation of cryptic two-character $? expressions is a thing that people will frequently complain about, dismissing Ruby as just another perl-ish line-noise language. Keep this chart handy. Note, a lot of these are useful when working with regexp code.
Note that there are some pre-defined constants at parse time, as well, namely
__FILE__ (current file)
and
__LINE__ (current line)
補充:ruby類型
Ruby Arrays:
Literals of Ruby Array are created by placing a comma-separated series of object references between square brackets. A trailing comma is ignored.
Example:
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Ruby Hashes:
A literal Ruby Hash is created by placing a list of key/value pairs between braces, with either a comma or the sequence => between the key and the value. A trailing comma is ignored.
Example:
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參考資料: 1. Ruby Programming/Syntax/Variables and Constants[ http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Variables_and_Constants] 2. Ruby Variables, Constants and Literals [ http://www.tutorialspoint.com/ruby/ruby_variables.htm]