Ruby Blocks
Block構成
A block consists of chunks of code.
You assign a name to a block.
The code in the block is always enclosed within braces ({}).
A block is always invoked from a function with the same name as that of the block. This means that if you have a block with the nametest, then you use the function?test?to invoke this block.
You invoke a block by using the?yield?statement.
語法：
block_name{
statement1
statement2
..........
}
Here you will learn to invoke a block by using a simple?yield?statement. You will also learn to use a?yield?statement with parameters for invoking a block. You will check the sample code with both types of?yield?statements.
使用yield調用代碼塊
yield語句 無參數
#!/usr/bin/ruby
def test
puts "You are in the method"
yield
puts "You are again back to the method"
yield
end
test {puts "You are in the block"}
結果
You are in the method
You are in the block
You are again back to the method
You are in the block
有參數
#!/usr/bin/ruby
def test
yield 5
puts "You are in the method test"
yield 100
end
test {|i| puts "You are in the block #{i}"}
結果
You are in the block 5
You are in the method test
You are in the block 100
在Block塊中，使用兩個豎線來表示接收的參數
test {|i| puts "You are in the block #{i}"}
如果接收多個參數
test {|a, b| statement}
Blocks and Methods:
塊與方法
def test
yield
end
test{ puts "Hello world"}
block作爲參數，使用"&"符號，被當作一個Proc對象來處理，利用自身的call方法來進行調用
def test(&block)
block.call
end
test { puts "Hello World!"}
結果
Hello World!
BEGIN and END Blocks
BEGIN Blocks
一般置於文件開始位置，優於其它代碼先執行，不受制於程序的邏輯運行。
END Blocks
程序結束時運行，END塊受制於程序的邏輯運行。
多個BEGIN Blocks時，按聲明順序執行
多個END Blocks時，正好相反
Ref:
Ruby Blocks
http://www.tutorialspoint.com/ruby/ruby_blocks.htm