Front-end Closures

[Florian Weimer]

On 02/06/2014 01:14 PM, Philip Herron wrote:

> I am trying to understand what way i could compile this in GCC can you
> do the following in GENERIC make a nested function decl kind of like a
> closure not quite sure what to do here.

It's just a statement expression.  The C front end supports them, so 
this might give you some idea how to implement them.

void main (void) {
      const char * item = "test";
      const double price = ({
          double ret_tmp;
          if (item == "salad") {
              ret_tmp = 3.50;
          }
          else if (item == "muffin") {
              ret_tmp = 2.25;
          }
          else {
              ret_tmp = 2.00;
          }
	 ret_tmp;
        });
}

To compile general closures, you have to apply a transformation called 
closure conversion.  GCC's nested functions only provide downward 
closures, and require an executable stack for trampolines on most 
architectures, which many systems do not support.

-- 
Florian Weimer / Red Hat Product Security Team