'raii' for structs

[Don Clugston]

I'm trying to get an implementation of floating-point rounding modes.
Normally, you set the rounding mode at the start of a function, and 
restore it at exit.

void somefunc()
{
  RoundingMode oldmode = setRoundingMode(ROUNDTOZERO);
:
:
:
  setRoundingMode(oldmode);
}

It's a classic RAII situation.
In C++, you'd do it as:

struct TemporaryRoundingMode
{
   RoundingMode oldmode;
   TemporaryRoundingMode(RoundingMode newmode)
     { oldmode = setRoundingMode(newmode); }
~TemporaryRoundingMode() { setRoundingMode(oldmode); }
};

void somefunc()
{
   TemporaryRoundingMode tempMode(ROUNDTOZERO);
   :
   :
}

How can it be done in D? It's only 2 asm instructions, you definitely do 
not want memory allocation happening.

Unfortunately you can't do

template TempRoundingMode(int mode)
{
   int oldmode = setRoundingMode(mode);
   scope(exit) int junk = setRoundingMode(oldmode);
}

void somefunc()
{
   mixin TemporaryRoundingMode!(ROUNDTOZERO);
   :
   :
}

which doesn't require you to name a useless temporary variable; but it 
doesn't work, because you can't use scope(exit) in a mixin. And you 
couldn't do variables that way, anyway.

Any ideas?