本節課主要4部分內容如下：
Ranges、Blocks and Procs、Random Numbers、Read/Write Text Files
4.1 Ranges
1)序列的定義：有起始值、結束值并且能夠獲取連續值的數據結構
2)使用.. 或者 ...聲明序列，
注意：..包含最大值,...不包含最大值
如 (
1..3) #結果是1,2,3
(1
3) #結果是1,2
3)ruby使用Range對象處理序列,(1..3)就作為一個Range對象.Range.to_a方法將Range轉換為Array
如 (1..10).to_a -> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
4)可以使用===判斷序列中是否有指定的值
如
(1..10) === 5 -> true
(1..10) === 15 -> false
(1..10) === 3.14159 -> true
('a'..'j') === 'c' -> true
('a'..'j') === 'z' -> false
4.2 Blocks and Procs
1)block是一組代碼段(grouping statements),它根據上下文的語義執行.
2)block 單行定義用{},多行定義使用do end
3)可以使用yield在方法中調用多次相關的block
如
def call_block
puts 'Start of method'
yield #在方法中調用block{puts 'In the block'}
yield
puts 'End of method'
end
call_block {puts 'In the block'}
4)code Block的返回值和方法類似,將最后一行的表達式作為返回值
5)block不是對象,但可以通過kernel的lambda方法轉換成Proc對象,
然后可以通過Proc的call調用block
prc = lambda {puts 'Hello'}
#將block{puts 'Hello'}轉換成對象
prc.call
#調用Proc對象的call方法執行block
注意:block有點回調函數的概念,它根據上下文執行具體的code
4.3 Random Numbers
1)ruby使用rand產生隨機數
2)rand(x)將生成大于0小于5的隨機整數
4.4 Read/Write Text Files
1) File.open 打開文件,可以指定打開方式
:'r' Read-only、(default); 'r+' Read/Write、'w' Write-only
2) 使用Find module來獲取文件夾下的內容 Find.find("./") #獲取當前路徑下的所有文件
3) Ruby Object Serialization
使用
Marshal.dump Saving an object and some or all of its components
使用
Marshal.load econstitute the object
4.5 總結
* Sequences have a start point, an end point, and a way to produce successive values in the sequence. In Ruby, these sequences are created using the ".." and "" range operators.
* The two dot form creates an inclusive range, and the three-dot form creates a range that excludes the specified high value.
* In Ruby, the sequence 1..100000 is held as a Range object containing references to two Fixnum objects.
* The .to_a method converts a Range to an Array.
* Another use of the versatile range is as an interval test: seeing if some value falls within the interval represented by the range. We do this using ===, the case equality operator.
* Ranges are not limited to integers or numbers. The beginning and end of a range may be any Ruby object.
* IMPORTANT: Ruby Code blocks are chunks of code between braces or between do- end that you can associate with method invocations.
* Code blocks may appear only in the source adjacent to a method call; the block is written starting on the same line as the method call's last parameter (or the closing parenthesis of the parameter list).
The code in the block is not executed at the time it is encountered. Instead, Ruby remembers the context in which the block appears (the local variables, the current object, and so on) and then enters the method.
* The Ruby standard is to use braces for single-line blocks and do- end for multi-line blocks. Keep in mind that the braces syntax has a higher precedence than the do..end syntax.
* Inside a method, you can call a Ruby block using the yield keyword with a value.
* You can provide parameters to the call to yield: these will be passed to the block. Within the block, you list the names of the arguments to receive the parameters between vertical bars (|).
* Blocks are not objects, but they can be converted into objects of class Proc. This can be done by calling the lambda method of the module Kernel.
* Remember you cannot pass methods into other methods (but you can pass procs into methods), and methods cannot return other methods (but they can return procs).
* The method to get a randomly chosen number in Ruby is rand.
* If you call rand, you'll get a float greater than or equal to 0.0 and less than 1.0. If you give it an integer parameter (by calling rand(5) ), you will get an integer value greater than or equal to 0 and less than 5.
* The File.open method can open a file in different modes like 'r' Read-only, starts at beginning of file (default); 'r+' Read/Write, starts at beginning of file; 'w' Write-only, truncates existing file to zero length or creates a new file for writing.
* File.open opens a new File if there is no associated block. If the optional block is given, it will be passed file as an argument, and the file will automatically be closed when the block terminates.
* Always close a file that you open. In the case of a file open for writing, this is very important and can actually prevent lost data.
* The seek method of class IO, seeks to a given offset an Integer (first parameter of method) in the stream according to the value of second parameter in the method. The second parameter can be IO::SEEK_CUR - Seeks to first integer number parameter plus current position; IO::SEEK_END - Seeks to first integer number parameter plus end of stream (you probably want a negative value for first integer number parameter); IO::SEEK_SET - Seeks to the absolute location given by first integer number parameter.
4.6 原文鏈接