Proposal: forward compatibility

[Jason House]

Denis Koroskin wrote:

> On Fri, 05 Sep 2008 09:57:40 +0400, Jason House
> <jason.james.house at gmail.com> wrote:
> 
>> D is an evolving language that does not restrict itself by requiring
>> backwards compatibility. Instead I propose that D adopt forward
>> compatibility...
>>
>> Specifically, allow D1 code to accept D2 code without doing extra
>> functionality. In D1, his would allow defining constants to be declared
>> with either const or invariant, object invariants to allow parenthesis,
>> and ignoring transitive const elements of type declarations.
>>
>> The goal is to not change the behavior of existing D1 code, but to
>> accept previously invalid D1 code. This should make the job of
>> maintaining a dual code base much easier.
> 
> I came up with the following constness solution:
> 
> First, define a Const!(T) template as follows:
> 
> ...
> 
> This would allow much easier D1/D2 migration without massive language
> changes.
> 
> What do you think?

I was worried that making a D1 compiler accept const in types declarations
would be a killer of the forward compatibility idea.  I think what you
propose for const type handling is a reasonable compromise.  It'd be easy
enough to write a Const!(T) and Invariant!(T) template.

I like how all the response to my proposal has been positive.  Sadly, it
can't go anywhere unless Walter likes the idea and he has yet to respond.