How to implement weakly typed variables in PHP
PHP is a weakly typed, dynamic language script. When declaring a variable, you do not need to specify the data type it holds. For example:
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Dynamic variables can be changed during runtime, and there is no need to declare the variable type before use.
Question 1. How does the Zend engine implement this weak type in C?
In fact, variables declared in PHP are stored in ZE using the structure zval.
First we open Zend/zend.h to see the definition of zval:
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Zend/zend_types.h:
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From the above code, we can see that _zvalue_value is the key part that actually saves data. Weakly typed variable declaration through union
Question 2. How does the Zend engine identify and store multiple data types in PHP?
_zval_struct.type stores the real type of a variable, and you can choose how to get the value of zvalue_value based on the type.
type value list (Zend/zend.h):
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Let’s look at a simple example:
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The most complex of these, and what is often used in developing third-party extensions, is "resources" Type".
In PHP, any variable that does not belong to PHP's built-in variable type will be treated as a resource and saved.
For example: database handle, open file handle, open socket handle.
The resource type will use lval, which is an integer indicator at this time. Then PHP will query the corresponding resource in a resource list built in PHP based on this indicator.
It is precisely because of ZE's processing method that PHP implements weak types, and for ZE, it always faces the same type zval.

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