D1 -> D2

[Walter Bright]

Steven Schveighoffer wrote:
> On Thu, 18 Nov 2010 14:19:12 -0500, Walter Bright 
> <newshound2 at digitalmars.com> wrote:
> 
>> Steven Schveighoffer wrote:
>>> My recommendation -- when you are ready, switch wholly to D2.  Don't 
>>> bother with compatibility, it's just not possible.
>>
>>  From what you wrote, it appears that most of the difficulties were in 
>> dealing with strings. Might I suggest:
>>
>> 1. Replace all occurrences of char[] with string.
>>
>> 2. Compile to find every place that mutable strings are used.
>>
>> 3. Refactor the code to clearly encapsulate where mutable strings are 
>> created and manipulated, and as the last step, cast them to string.
> 
> But string is not always what is desired.  It depends on the library.

Right.


> Tango uses mutable arrays everywhere because it prefers not to use the 
> heap as much as possible.  For example, something might take a char[] 
> buffer, and a function may pass in a stack-allocated array for the 
> buffer.  Changing this to string is useless.

That's where refactoring comes in. I haven't looked at the Tango code, but 
there's a big difference between "using mutable arrays everywhere" and actually 
needing to mutate them. Only the latter needs to be char[], and the boundaries 
between the two are bridged with a .idup or a cast(string).

If Tango is relying on string literals to be char[], i.e. be mutable, this is a 
serious bug and will cause seg faults. So, this issue must have already been 
dealt with in Tango, and codifying string literal types as "string" rather than 
"char[]" should not negatively impact it.

And lastly, if there are APIs in tango that accept char[] and leave the caller 
perplexed about whether the API will mutate the string or not, that is something 
that using string for the non-mutating ones nicely resolves.