PHP singleton mode (responsibility mode)

Simply put, an object (before learning design patterns, you need to understand object-oriented thinking) is only responsible for a specific task;

Single instance class:

1. Constructor It needs to be marked as private (access control: to prevent external code from using the new operator to create objects). The singleton class cannot be instantiated in other classes and can only be instantiated by itself;

2. Have a saved class Static member variables of the instance

3. Have a public static method to access this instance (the getInstance() method is commonly used to instantiate a singleton class, and the instanceof operator can be used to detect whether the class has been instantiated. )

In addition, you need to create a __clone() method to prevent the object from being copied (cloned)

Attachment
trigger_error() Function creates user-level error messages. 
trigger_error() The function can be associated with the built-in error handler, or a user-defined function can be used as a new error handler (set_error_handler()). 
trigger_error(errormsg,errortype);
Parameters
Description
errormsg
Required. Specifies the error message. Maximum length 1024 bytes. 
errortype
 Optional. Specifies the error type. Possible values: E_USER_ERRORE_USER_WARNINGE_USER_NOTICE (default) 

## Simply put, an object (before learning design patterns, you need to know more about object-oriented Thought) is only responsible for a specific task; 
 Singleton class: 
1. The constructor needs to be marked as private (access control: prevent external code from using the new operator to create objects), singleton A class cannot be instantiated in other classes, but can only be instantiated by itself;
2. Have a static member variable that saves an instance of the class
3. Have a public member variable that accesses this instance Static method (the getInstance() method is commonly used to instantiate a singleton class, and the instanceof operator can be used to detect whether the class has been instantiated) 
In addition, you need to create a __clone() method to prevent the object from being copied ( Clone) 
Attached
trigger_error() Function creates a user-level error message. 
trigger_error() The function can be associated with the built-in error handler, or a user-defined function can be used as a new error handler (set_error_handler()). 
trigger_error(errormsg,errortype);
ParametersDescriptionRequired. Specifies the error message. Maximum length 1024 bytes.  Optional. Specifies the error type. Possible values: E_USER_ERRORE_USER_WARNINGE_USER_NOTICE (default) 
errormsg
errortype
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