Safe cast away from immutable

[anonymous via Digitalmars-d]

On 08.02.2016 22:14, Iakh wrote:
> Is all prams being const(but not immutable) not enough for
> function to be Pure?

The hidden `this` parameter must be const, too. And mutable indirections 
in the return type must be considered.

This article explains it in detail:
http://klickverbot.at/blog/2012/05/purity-in-d/