function_exists（）是否缓存其查询？

Question

I wonder to know does function_exists() cache its queries internally?

Answer 1

No, it does not. It just checks whether the function is defined in the function table. Simple enough.

However, the Zend Opcache extension may optimize out some calls to function_exists() and certain other functions which can in some cases be evaluated at compile time. (It only optimizes out calls to function_exists() where the function is defined internally by PHP, or by an extension.)