legacy code retreat's triva game : the D version

[bearophile]

Meta:

> I know immutable is a good thing, but don't you think 
> `immutable _` is a bit unnecessary in this case?

Some answer, choose the one you prefer:

1) Yes, it's totally useless because the _ variable is not even 
used inside the loop body! So sorry, I'm always so pedantic.

2) It's necessary, don't you see that? You don't need to mutate 
that variable, so it's better for it be immutable. A simple rule 
to follow is to make const/immutable all variables that don't 
need to mutate, to make code simpler and safer. There's no real 
reason to break that general rule in this case.

3) Just like the integer '5' a range of values as 0 .. 1000 is an 
immutable value. So a variable that scans such range should be 
immutable. If you really want to mutate such variable you should 
add a modifier like "mutable" or "mut" or something. Another 
common trap in D coding is iterating on an array of structs with 
foreach, mutating the current struct and forgetting that you are 
mutating only a _copy_ of the items. Unfortunately there is no 
mutable keyword in D, and Walter rejected all this idea. So the 
next best thing it to always put "immutable" at the foreach 
variable, unless you want to mutate it or if you can't use 
const/immutable for some other reason.

Probably I can invent you more creative answers if you want.

Bear hugs,
bearophile