Stepping back and looking at constness from another angle.

[Reiner Pope]

Another problem with const by default came to mind. Consider the 
following code, with const-not-by-default:

void foo( ref const(char)[] c)
{
     c = c[1..$];
}

I would hate to see this in const-by-default, which would try to wrap a 
const( ) around the whole type. To counter that, you would probably have 
to write some mess like

void foo ( mutable( ref const(char)[] ) c )
{
     c = c[1..$];
}

   -- Reiner