One of my super short reviews on the books I read in my My Way to PHP series.
Mastering the SPL Library by Joshua Thijssen
My first problem was the title which literally says: “Mastering the Standard PHP Library 
Library”. Also the source code is in gray which can be hard to read. But after that this book was a treat!
What I really liked about the book is the depth. The author goes into the details. Shows how the hashtable in PHP is implemented. Then for each data structure he shows its complexity. The following chapters are also excellent. He shows different classes of SPL, shows why to use them and how.
In my opinion, an excellent book which restored my faith in php[architect]. Definitely recommended!