constructer of class in ruby_Ruby_编程开发_程序员俱乐部

1. for a string class:

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s = "foobar" ?# this a literal constructor for strings using double quotes

s.class ? => String

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we see here that string respond to the method "class", and return the class it belong to.

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2. instead of using literal constructor, we can use named constructor, so call the new method on the class name:

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s = String.new("foobar")

s.class

s == "foobar" ? ? => ? ?true

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3. array works the same way:

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a = Array.new([1,2,3])

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4. hash is different:

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h = Hash.new ? => {} ? # this will create a new empty hash

h[:foo] ? ? ?=> nil

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but if you specify a value in the constructor call, this value will be the default value for the hash, so for each nonexistent key, it is value will be this value instead of nil.

h = Hash.new(0)

h[:foo] ? ? => ? 0

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5. in the definition of the constuctor, the method name is?

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def initialize(param)

.......

end

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6. there is superclass method that will be useful:

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s = String.new("foobar")

s.class ? => ? String

s.class.superclass ? ?=> ?Object

s.class.superclass.superclass ? => ?BasicObject

s.class.superclass.superclass.superclass ? => ?nil

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This pattern is true of every Ruby object: trace back the class hierarchy far enough and every class in Ruby ultimately inherits from?monospace; vertical-align: baseline; color: #006400; padding: 0px; margin: 0px;">BasicObject, which has no superclass itself. This is the technical meaning of “everything in Ruby is an object”.