Mixin mystic

[Georg Wrede]

On December 14, Nick Sabalausky wrote:
> That explains a certain mystery I encountered in a library I wrote. 
> Everything *seemed* like it should have worked with "scope" instead of 
> "auto" but it never did. The variables that were mysteriously unconvertable 
> to "scope" were declared in a mixin.
> 
> This makes me wonder though: should mixins be implicitly creating a new 
> scope at all? Clearly there are cases where it's desireable to not have that 
> implicit scope, and with the current behavior I don't see a workaround. Are 
> there cases where an implicit new scope would be desired? If so, could those 
> cases be sufficiently worked around by explicitly creating a new scope in 
> the mixin? 

For some reason, nobody seemed to have read this question.

One would think that the mixin not creating a new scope would be what 
the programmer expects. Or at least hopes...



On a related note, seems an object of a scope variable in a mixin 
doesn't get destructed. Is this a result of some hack, or intended behavior?

Below, instance "scope_mixi_a" never gets destructed.

======================================================

import std.stdio;

class Ob
{
     string myname;
     this(string s)
     {
         myname = s;
         // writeln("Ob ", myname, " created.");
     }

     ~this() {writeln("Ob ", myname, " destructed.");}
}

template mixi()
{
     scope mixi_a = new Ob("scope_mixi_a");
     auto mixi_b = new Ob("auto_mixi_b");
}

void main()
{
     scope x = new Ob("scope_x");
     auto  y = new Ob("auto_y");
     {
         scope a = new Ob("scope_a");
         auto  b = new Ob("auto_b");

         mixin mixi;

         scope c = new Ob("scope_c");
         auto  d = new Ob("auto_d");
         writeln(" -- last line of inner scope");
     }
     scope z = new Ob("scope_z");
     auto  u = new Ob("auto_u");
     writeln(" -- last line of outer scope");
}

======================================================
Output:

  -- last line of inner scope
Ob scope_c destructed.
Ob scope_a destructed.
  -- last line of outer scope
Ob scope_z destructed.
Ob scope_x destructed.
Ob auto_u destructed.
Ob auto_d destructed.
Ob auto_mixi_b destructed.
Ob auto_b destructed.
Ob auto_y destructed.