improving scope(finally/success)

[Idan Arye via Digitalmars-d]

On Thursday, 3 December 2015 at 11:41:29 UTC, Tomer Filiba wrote:
> it'd be really helpful if scope() statements got hold of the 
> return value or exception, e.g.,
>
> scope(success, retval) {
>     writeln("the retval is", retval)
> }
>
> scope(failure, ex) {
>     if(typeid(ex) == typeid(MyException)) {
>         callTheCops();
>     }
> }
>
> it would make logging very easy, and since these statements are 
> basically code-rewrites i don't suppose it would be hard to 
> implement. from a syntax point of view:
>
> scope(succes[, VARNAME])    // where VARNAME would be the 
> return value (a const tmp variable?)
> scope(failure[, VARNAME])   // where VARNAME would be hold the 
> exception (a Throwable)
>
> i mean, code such as
>
> int f() {
>     scope(exit) writeln("bye");
>     return 5;
> }
>
> is rewritten as something like
>
> int f() {
>     try {
>         auto tmp = 5;
>     }
>     finally {
>         writeln("bye");
>     }
>     return tmp;
> }
>
> so `tmp` is already there for the finally clause (modulo 
> scoping issues)

int foo(bool cond) { // scope 1
    { // scope 2
        scope(success, retval) {
            writeln("the retval is", retval)
        }
        if (cond) { // scope 3
            return 1;
        }
    }
    return 2;
}


`foo(true)` should obviously print "the retval is 1", but what 
should `foo(false)` print? It's `scope(success)` block should run 
when it exists scope 2, but the return value is only determined 
at the end of scope 1.