are scope guards (scope(exit, success, failure)) zero-cost abstractions?

[Timothee Cour]

I'm curious whether scope guards add any cost over the naive way, eg:

```
void fun(){
  ...
  scope(success) {bar;}
  ...
}
```

vs:

```
void fun(){
  ...
  if(foo1){
    bar;  // add this before each return
    return;
  }
  ...
  bar;
  return;
}
```

For scope(success) and scope(failure), the naive way would anyway
involve try/catch statements but what about scope(exit)? Does the
zero-cost exception model (zero cost being for non-thrown exceptions)
guarantee us that scope(success) has 0 overhead over naive way?