Ruby Block

grammar

block_name{
   statement1
   statement2
   ..........
}

Here you will learn how to use a simpleyieldstatement to call the block. You will also learn how to use theyieldstatement with parameters to the called block. In the example, you will see two types ofyieldstatement.

yieldstatement

Let's look at an example yield statement:

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

def test
   puts "在 test 方法内"
   yield
   puts "你又回到了 test 方法内"
   yield
end
test {puts "你在块内"}

try it"

Examples of the above operating results as follows:

在 test 方法内
你在块内
你又回到了 test 方法内
你在块内

You can also pass yield statement with parameters. Here is an example:

#!/usr/bin/ruby
# -*- coding: UTF-8 -*-

def test
   yield 5
   puts "在 test 方法内"
   yield 100
end
test {|i| puts "你在块 #{i} 内"}

try it"

Examples of the above operating results as follows:

你在块 5 内
在 test 方法内
你在块 100 内

Here, after theyieldstatement followed parameters. You can even pass multiple parameters. In the block, you can place a variable between two vertical bars to accept the parameters. Thus, in the above code, yield 5 statement is passed as a parameter to the value of 5 test pieces.

Now, look at the following statement:

test {|i| puts "你在块 #{i} 内"}

Here, the value of 5 will receive the variable i. Now, we put observe the following statement:

puts "你在块 #{i} 内"

This puts the output statement is:

你在块 5 内

If you want to pass multiple parameters, then theyieldstatement is as follows:

yield a, b

At this time, as shown in the block:

test {|a, b| statement}

Parameters separated by commas.

Blocks and methods

You have seen between the block and the method of how interrelated. You typically use the yield statement calls the block from the method having the same name. Therefore, the code is as follows:

#!/usr/bin/ruby

def test
  yield
end
test{ puts "Hello world"}

This example is the simplest way to achieve the block. You use theyieldstatement calls the test block.

But if the last parameter before the method with & then you can the method is passed a block, and this block may be assigned to the last parameter. If the * and & also appear in the parameter list, & should be placed on the back.

#!/usr/bin/ruby

def test(&block)
   block.call
end
test { puts "Hello World!"}

try it"

Examples of the above operating results as follows:

Hello World!

BEGIN and END blocks

Every Ruby source file can declare when code blocks (BEGIN block) when the file is loaded to run, and after the program finishes executing code blocks to run (END block).

#!/usr/bin/ruby

BEGIN { 
  # BEGIN 代码块
  puts "BEGIN 代码块"
} 

END { 
  # END 代码块
  puts "END 代码块"
}
  # MAIN 代码块
puts "MAIN 代码块"

A program can contain multiple BEGIN and END blocks. BEGIN block is executed in the order in which they appear. END blocks as they appear in reverse order. When executed, the above program produces the following results:

BEGIN 代码块
MAIN 代码块
END 代码块