Knowledge of the blocks in Ruby

Source: Internet
Author: User

This article mainly introduces the knowledge of the blocks in Ruby, including yield statements and begin/end blocks, and so on, the friends you need can refer to the

Grammar:

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1 2 3 4 5 block_name{statement1 statement2 .....}

Here, you will learn how to call blocks by using a simple yield statement. You will also learn to use the yield statement to have parameter call blocks. The sample code that will be checked, the two types of yield statements.

Yield statement:

Let's take a look at an example in the yield statement:

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1 2 3 4 5 6 7 8 9 #!/usr/bin/ruby def Test puts "you are in the method" yield puts "you are again then to the method" yield end test {puts "are in"}

This will produce the following results:

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1 2 3 4 You are are in the "method" you are in the blocks you are again the

You can also pass the argument with the yield declaration. Here is an example:

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1 2 3 4 5 6 7 8 #!/usr/bin/ruby def Test yield 5 puts "you are in ' method test" yield-end test {|i| puts ' you are in the ' block #{ i} "}

This will produce the following results:

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1 2 3 You are are in the "Block 5" are in the "method test" you are in the Block 100

Here the yield statement is written to follow the arguments. You can even pass multiple parameters. A variable that is placed between two vertical lines in the block (| |) The parameters received. Therefore, in the above code, the YIELD5 statement takes the test block as a parameter value of 5.

Now look at the following statement:

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1 Test {|i| puts ' you are in the ' Block #{i} '}

Here, the value in the variable i is 5. Now observe the following puts statement:

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1 Puts "You are in the Block #{i}"

The output of the puts statement is:

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1 are in the Block 5

If you want to exceed one argument, then the yield statement becomes:

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1 Yield A, b

So the block is:

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1 Test {|a, b| statement}

These parameters are separated by commas.

Blocks and methods:

We've seen how to associate a block with a method. Typically, the call block has a method with the same name from the block by using the yield statement. Therefore, write:

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1 2 3 4 5 6 #!/usr/bin/ruby def test yield end test{puts "Hello World"}

This example is the simplest way to implement a block. Call block test uses the yield statement.

However, if the last parameter's method is preceded by an ampersand, the block will be assigned to the last parameter by this method of a block.

* and & in the parameter list & is still in the back.

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1 2 3 4 5 6 7 8 9 10 #!/usr/bin/ruby def test (&block) Block.call end test {puts "Hello world!"} This'll produce following Result:hello world!

BEGIN and End Blocks

After each ruby source file can be declared as a file to be loaded to run (begin block), the program has finished (end block).

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1 2 3 4 5 6 7 8 9 10 11 12-13 #!/usr/bin/ruby begin {# Begin block code puts ' begin code block '} end {# End block code puts ' end ' code block} # Main block code puts ' main code block '

A program may include multiple begin and end blocks. The begin blocks are executed in the order in which they are encountered. End blocks are executed in reverse order. When the above program executes, the following results are produced:

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