Php collection: type constraints

Suddenly, I don't want to do anything, just like my uncle .. However, the habit of writing a blog every workday cannot be broken .. So let's have a try today.

PHP has been in use for almost two years, but this was the first time I saw it. Suddenly, I felt like I had gone back to the five dregs of the war.
Open the official document "type constraints" to explain it very clearly.
There are four types in total: Class Name, interface, array, callable (from PHP 5.4)
No int string can be used ..
The example and other PHP manuals have already been very detailed. I am also too lazy to write it. This is just a point of knowledge and I will take a look at it ..

In fact, I haven't written PHP for a long time. Now I want to read all the major frameworks, but I doubt that I will actually use PHP ,,