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Abstract

To add dynamic scoping to C++, the C++ equivalent of Elisp's "unwind-protect" and Java's "finally" mechanism needs to be used. In the absence of exceptions this is very simple to code:

int global;

void foo()
{
    int global_temp = global;
    global = new_value;

    /* rest of foo method */

    global = global_temp;
}

In the case that exceptions are used then destructors must be used, using a design pattern that C++ creator Bjarne Stroustrup calls Resource Acquisition Is Initialization (or R.A.I.I. for short). An alternative approach to this one is to prefer to use C++ preprocessor macro calls to ordinary function/method calls. Here is an example where the F3 and F4 macro functions can access the variable x from the function f1.

#define F4 \
call_other_1(x);  \

#define F3 \
call_other_2(x)   \

#define F2 \
F3();         \
F4();         \

void f1()
{
   int x;
   F2();
}