D Library Breakage

[Steven Schveighoffer]

On 4/13/18 4:15 PM, Steven Schveighoffer wrote:

> I don't know if the compiler can determine if a version statement 
> affects the layout, I suppose it could, but it would have to compile 
> both with and without the version to see. It's probably an intractable 
> problem.

Even when the layout is affected, it may not be a problem.

For example, in std.internal.cstring, we have this:

     version(unittest)
     // the 'small string optimization'
     {
         // smaller size to trigger reallocations. Padding is to account for
         // unittest/non-unittest cross-compilation (to avoid corruption)
         To[16 / To.sizeof] _buff;
         To[(256 - 16) / To.sizeof] _unittest_pad;
     }
     else
     {
         To[256 / To.sizeof] _buff; // production size
     }

This results in the same size type whether you compile with unittests or 
not.

Even if the compiler can tell "something's not the same", it may not be 
a problem, as in this case.

-Steve