Detailed introduction to PHP type constraints (with code)

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Introduction: The so-called type constraint means that when defining a variable, its type must be specified, and the variable can only store data of this type in the future. Although PHP is a weakly typed language, it already supports type constraints in PHP 5, including objects, interfaces, and arrays. It supports scalar type constraints after PHP 7. Here are a few examples.

Scalar type, array

Specify the type in the parameter. If it is inconsistent, a catchable fatal error will be thrown

      
As shown above , the same is true for scalar types
      

      
Objects, interfaces
      
Type constraints can also be specified as objects or interfaces. First define aHumaninterface, andBoyandGirltwo classes implement the interface respectively
      

      
Next, create a new class to test
      
say(); } /** * Girl 对象类型约束 * @param Girl $girl */ public function girlSay(Girl $girl) { $girl->say(); } /** * Human 接口类型约束 * @param Human $obj */ public function humanRun(Human $obj) { $obj->run(); } } $obj = new Action(); $obj->boySay(new Boy());// a boy say echo '
'; $obj->girlSay(new Girl());// a girl say echo '
'; $obj->humanRun(new Boy());// a boy run echo '
'; $obj->humanRun(new Girl());// a girl run
      
When the type constraint is a specific objectBoyorGirl, only the required object can be passed in. When the type constraint is interfaceHuman, you can pass in the classBoyorGirlthat implements the interface.
      
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