方法内的局部变量，并分配一个函数？

I came across some codes that for me it looked confusing, although I looked in many places googling, I could not find the exact answer for my question. In hope to know what's going on with this code I'm here, asking if there's a good explanation for me, so I would not only know how to do it but, learn what it does as well!I came across some codes that for me it looked