Re: try/catch idiom in std.datetime

[Shammah Chancellor]

On 2013-11-22 02:07:36 +0000, growler said:

On Friday, 22 November 2013 at 01:49:11 UTC, Shammah Chancellor wrote:

On 2013-11-18 06:32:46 +0000, Andrei Alexandrescu said:

1. Fix scope(failure) and then use it.

Andrei

Huh? Scope failure has no purpose here. It does not CATCH the exception and prevent it from bubbling up the call chain. Try/catch does do this.

-Shammah

It does if you return from the scope(failure) block. The problem is you cannot mark the function as "nothrow"

For example:
---
void throwingFunction() {
     throw new Exception("damn!");
}

void someFunc() // nothrow
{
     scope(failure) {
         writeln("Failed in someFunc()");
         return;
     }
     throwingFunction();
}

void main() {
     try {
         someFunc();
         writeln("Yay, someFunc() is nothrow");
     } catch(Exception e) {
         writeln("An exception in main!");
     }
}

Output:

Failed in someFunc()
Yay, someFunc() is nothrow.
---

But you cannot mark someFunc() as nothrow.

What!?  That shouldn't even be legal code!   See below for why:

void throwingFunction() {
    throw new Exception("damn!");
}

void someFunc() // nothrow
{
   scope(failure) { writeln("What?");} <-- NEVER EXECUTED?!
    scope(failure) {
        writeln("Failed in someFunc()");
        return;
    }
    throwingFunction();
}

void main() {
    try {
        someFunc();
        writeln("Yay, someFunc() is nothrow");
    } catch(Exception e) {
        writeln("An exception in main!");
    }
}