To shed some light on the practice of using `let` vs. `var`, an excerpt from the book by Apple:

“If a stored value in your code is not going to change, always declare it as a constant with the let keyword. Use variables only for storing values that need to be able to change.”

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/us/jEUH0.l

Thanks Andrew, I am updating the posts as I learn more. We're all still learning.

Let is fine for defining constants, but it should also be used whenever possible for two reasons:

1. It gives you additional safety against accidental reassignment.

2. It gives the compiler a major optimization hint since the value is not a variable.

The latter isn't really true when it comes to local variables. Compilers are pretty good at figuring that sort of thing out these days.

It is one of the reasons stated by Apple at today's WWDC session.