'const' and 'in' parameter storage classes

[Adam D. Ruppe via Digitalmars-d-learn]

The scope storage class means you promise not to escape any 
reference to the data. This isn't enforced but it is similar in 
concept to Rust's borrowed pointers - it may someday be 
implemented to be an error to store them in an outside variable.

Only use 'in' if you are looking at the data, but not modifying 
or storing copies of pointers/references to it anywhere in any 
way.