First Draft: Static Single Assignment

[Walter Bright]

What you're proposing is "head const", which is what C and C++ have. D has 
"transitive const". Try to change the type system to support head const is 
extremely destructive, and likely to be terribly confusing.

That's why "final" is a storage class, which sidesteps the issue.

The C++ method of making references is part of the type system and is extremely 
awkward.