PHP single-instance object form

PHP Singleton Object mode
?

Suppose we need to write a class to manipulate the database and meet the following requirements:

①sqlhelper class can have only one instance (not many)
The ②sqlhelper class must be able to create this instance on its own
③ must provide this instance to the entire system on its own, in other words: multiple objects share a chunk of memory, for example, object a sets some property values, and the object B,c can also access these property values (the end example is a good illustration of the problem)

? Turn from: php? singleton mode?-? God horse?-? cloud code space? http://yuncode.net/article/a_524a37fc4bfb716

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