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digitalmars.D - Return in finally

reply "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
While programatically porting Java ...

A finally block cannot contain another try/catch block. This is allowed
in Java. The solution i use is this:

int f(){
  try{
  } finally {
    (){ // start definition of an unnamed function literal
      try{
      } finally {
        // (1)
      }
    }(); // call it.
  }
  return 1;
}

Now, i have the first time the situation where at (1) a return statement
 occurs. This is not allowed in an a finally block at all [2], and
withing the function literal it would not end the surrounding function.

Any idea, how to simulate
1.) try/catch/finally in a finally
2.) make a return from within a finally
??


[2] not allowed in D, but it is allowed in Java
Mar 07 2007
next sibling parent reply BCS <BCS pathlink.com> writes:
Frank Benoit (keinfarbton) wrote:
 While programatically porting Java ...
 
 A finally block cannot contain another try/catch block. This is allowed
 in Java. The solution i use is this:
 
 int f(){
   try{
   } finally {
     (){ // start definition of an unnamed function literal
       try{
       } finally {
         // (1)
       }
     }(); // call it.
   }
   return 1;
 }
 
 Now, i have the first time the situation where at (1) a return statement
  occurs. This is not allowed in an a finally block at all [2], and
 withing the function literal it would not end the surrounding function.
 
 Any idea, how to simulate
 1.) try/catch/finally in a finally
 2.) make a return from within a finally
 ??
 
 
 [2] not allowed in D, but it is allowed in Java

try { ... } finally { ... return; ... } | | v try { ... } catch(Object e) { ... return; ... throw e; } bad practice in hand work, but this is auto gen code.
Mar 07 2007
parent reply "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
If i understand your idea right...

class FinallyException : Object {} // Special excecption to enter a
finally block.
class Throwable : Exception {} // Base of all Java Exceptions

Now, instead of finally use only catch blocks

catch( FinallyException fe ){
 ...
}

Hm, i need to think more about it...
The FinallyException can be used to transport a thrown exception
At (1),(2) and (3) a return(val) or throw can happen.

// Java ==========================
try{
  // (1)
} catch( IOException e ){
  // (2)
} finally {
  // (3)
}

// D ==========================
auto fe = new FinallyException();
try{
  try{
    // (1)
    throw fe;
  } catch( IOException e ){
    try{
    // (2)
    } catch( Object e ) {
      fe.store(e);
      throw fe;
    }
  }

}catch( FinallyException fe ){
  // (3)
}
fe.throwIfHasException();


Does this work? oh, my brain hurts :)

Another thought, what about the performance, if an exception is always
thrown to reach the "finally" block? is that an issue?
Mar 07 2007
next sibling parent "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
// D ==========================
int func(){
  ...
  {
    Tioport_ResultState!(int) tioport_result_001;
    try{
      try{
        // (1)
      } catch( IOException e ){
        // (2)
      }
    } catch( Object e ) {
      // catch and store for rethrow after Finally_001
      tioport_result_001.setException( e );
    }
    Finally_001:
    {
      // (3)
    }
    tioport_result_001.checkException(); // throw if one was stored
    return tioport_result_001.get();
  }
}

In (1) und (2) replace all "return;" with "goto Finally_001;". "return
expr;" with "{ tioport_result_001.set( expr ); goto Finally_001; }"

If in (3) a return or throw occurs, it hides previous returns/throws,
like java does.

This approach do not throw an exception in normal run.

What do you think?
Do I miss a less complicated way?
Mar 07 2007
prev sibling parent BCS <BCS pathlink.com> writes:
Frank Benoit (keinfarbton) wrote:
 If i understand your idea right...
 
 class FinallyException : Object {} // Special excecption to enter a
 finally block.
 class Throwable : Exception {} // Base of all Java Exceptions
 
 Now, instead of finally use only catch blocks
 
 catch( FinallyException fe ){
  ...
 }
 

There is no need for special excption types, Object will catch everything. Err. However it won't catch a normal exit. Fud, It's not quite as clean as I thought.
Mar 07 2007
prev sibling parent reply Ary Manzana <ary esperanto.org.ar> writes:
Frank Benoit (keinfarbton) escribió:
 Any idea, how to simulate
 2.) make a return from within a finally
 ??

Maybe you can do something like this: Java ------------------------------------------------- int func() { try { } finally { return 1; } } ------------------------------------------------- D ------------------------------------------------- import std.boxer; int func() { Box finallyReturn; try { } finally { finallyReturn = box(1); } if (finallyReturn.type !is null) { return unbox!(int)(finallyReturn); } } ------------------------------------------------- You have to be careful, though. After every block that has a return statement you have to proceed only if the box's type is null. For example: Java ------------------------------------------------- int func() { try { } finally { if (someCondition) { return 1; } doSomeStuff(); return 2; } } ------------------------------------------------- D ------------------------------------------------- import std.boxer; int func() { Box finallyReturn; try { } finally { if (someCondition) { finallyReturn = box(1); } if (finallyReturn.type is null) { doSomeStuff(); finallyReturn = box(2); } } if (finallyReturn.type !is null) { return unbox!(int)(finallyReturn); } } ------------------------------------------------- Does this work?
Mar 07 2007
parent "Frank Benoit (keinfarbton)" <benoit tionex.removethispart.de> writes:
 Does this work?

yes, this would handle the return, but it would not allow a second try/catch in the finally block. What i use now is this: // D ========================== int func(){ ... { bool tioport_stat_set_1; int tioport_stat_val_1; Object tioport_stat_exc_1; try{ try{ // (1) tryend_1:; } catch( IOException e ){ // (2) } catchend_1:; } catch( Object e ) { tioport_stat_exc_1 = e; } { // (3) } if(tioport_stat_exc_1 !is null) throw tioport_stat_exc_1; if(tioport_stat_set_1) return tioport_stat_val_1; } } In (1) und (2) replace all "return expr;" with { tioport_stat_set_1 = true; tioport_stat_val_1 = expr; // if has a return val goto tryend_1; // or catchend_1 } Now the finally block is a normal code block. It is possible to have more try/catch in the finally block. It is possible to return/throw from the finally block
Mar 07 2007