ruby hash方法

Hash.default(key = nil)方法 (Hash.default(key=nil) Method)

In this article, we will study about Hash.default(key=nil) Method. The working of this method can be predicted with the help of its name but it is not as simple as it seems. Well, we will understand this method with the help of its syntax and program code in the rest of the content.

在本文中，我们将研究Hash.default(key = nil)方法 。 可以借助其名称来预测此方法的工作，但是它并不像看起来那样简单。 好了，我们将在其余内容中借助其语法和程序代码来理解此方法。

Method description:

方法说明：

This method is a public instance method that is defined in the ruby library especially for Hash class. This method works in a way that it returns the default value but now you will be thinking when this method will return the default value. This method will return the default value when the user is trying to access the value of key or simply key which is not available in the hash or you can say that which is not a part of the hash object. The method will print the default value instead of returning 'nil'.

此方法是在ruby库中定义的公共实例方法，特别是针对Hash类。 此方法以返回默认值的方式工作，但是现在您将考虑此方法何时将返回默认值。 当用户尝试访问哈希值中不可用的key值或key值时，此方法将返回默认值，或者您可以说那不是哈希对象的一部分。 该方法将打印默认值，而不是返回'nil' 。

Syntax:

句法：

    Hash_object.default
or
Hash_object.default(object)

Argument(s) required:

所需参数：

Passing value in this method is optional. If you are passing a value then that value can be an object of any class.

在此方法中传递值是可选的。 如果要传递值，则该值可以是任何类的对象。

Example 1:

范例1：

=begin
Ruby program to demonstrate default method
=end
hsh = Hash.new("Not available")
hsh["color"] = "Black"
hsh["age"] = 20
hsh["school"] = "Angels' Academy Haridwar"
hsh["college"] = "Graphic Era University"
puts "Hash default implementation"
puts "Hash contents are : #{hsh}"
puts "default value : #{hsh.default}"

Output

输出量

Hash default implementation
Hash contents are : {"color"=>"Black", "age"=>20, "school"=>"Angels' Academy Haridwar", "college"=>"Graphic Era University"}
default value : Not available

Explanation:

说明：

In the above code, you can observe that we have set a default value with the help of the new method. We are accessing that default value with the help of the default method. The default value is "Not available" and this value will be returned whenever the key is not found in the hash object.

在上面的代码中，您可以看到我们已经在new方法的帮助下设置了默认值。 我们正在借助默认方法访问该默认值。 默认值为“不可用” ，只要在哈希对象中找不到密钥，就会返回此值。

Example 2:

范例2：

=begin
Ruby program to demonstrate default method
=end
hsh = Hash.new { |hash, key| hsh[key] = "Hello : #{key}" }
hsh["color"] = "Black"
hsh["age"] = 20
hsh["school"] = "Angels' Academy Haridwar"
hsh["college"] = "Graphic Era University"
puts "Hash default implementation"
puts "Hash contents are : #{hsh}"
puts "default value : #{hsh.default(2)}"

Output

输出量

Hash default implementation
Hash contents are : {"color"=>"Black", "age"=>20, "school"=>"Angels' Academy Haridwar", "college"=>"Graphic Era University"}
default value : Hello : 2

Explanation:

说明：

In the above code, you can observe that we have set a default value with the help of the new method by passing a block into it. We are accessing that default value with the help of the default method. The default value is "Hello: key" and this value will be returned whenever the key is not found in the hash object. We are passing the key along with the method and that key will be returned along with the value when the key is missing.

在上面的代码中，您可以观察到，借助于将新的块传递给新方法，我们已经设置了默认值。 我们正在借助默认方法访问该默认值。 默认值为“ Hello：key” ，只要在哈希对象中未找到该键，就会返回该值。 我们将键与方法一起传递，当键丢失时，键将与值一起返回。

翻译自: https://www.includehelp.com/ruby/hash-default-key-nil-method-with-example.aspx

ruby hash方法