On 07/25/2012 12:29 PM, Neil Toronto wrote:
What if TR had a notion of const-ness, like in C? Suppose (Vectorof A) is a subtype of (Const-Vectorof B) when A is a subtype of B, and (Const-Vectorof A) is never a subtype of (Vectorof B).
In C, "const" is a contract on the function type, not on the parameter data type. This can be a very useful contract. Once const applies to a variable, it becomes sticky and requires an explicit (and easily searched) const_cast downgrade to become mutable again.
This can be useful and quite annoying. Using const in one spot often causes a snowball effect where it must be manually propagated to other function prototypes. C++ allows certain fields to be marked as mutable, even when the containing object is const. A more dynamic language might be able to decorate the value instead of the function, or at least infer const-ness where possible?
- Daniel _________________________ Racket Developers list: http://lists.racket-lang.org/dev
