.NET iterator to wrap throwing API

Question

I have a class with an API that allows me to ask for objects until it throws an IndexOutOfBoundsException.

I want to wrap it into an iterator, to be able to write cleaner code. However, I need to catch the exception to stop iterating:

static IEnumerable<object> Iterator( ExAPI api ) {
    try {
       for( int i = 0; true; ++i ) {
          yield return api[i]; // will throw eventually
       }
    } 
    catch( IndexOutOfBoundsException ) {
       // expected: end of iteration.
    }
}

But...

When used with expression, a yield return statement cannot appear in a catch block or in a try block that has one or more catch clauses. For more information, see Exception Handling Statements (C# Reference).Statements (C# Reference). (from the msdn)

How can I still wrap this api?

Answer 1

You simply need to move the yield return statement outside of the try block, like this:

static IEnumerable<object> Iterator( ExAPI api ) {
   for( int i = 0; true; ++i ) {
        object current;
        try {
            current = api[i];
        } catch(IndexOutOfBoundsException) { yield break; }

        yield return current;
    } 
}

Answer 2

You can wrap the simple operation of getting the object into a separate function. You can catch the exception in there:

bool TryGetObject( ExAPI api, int idx, out object obj )
{
    try
    {
        obj = api[idx];
        return true;
    }
    catch( IndexOutOfBoundsException )
    {
        return false;
    }        
}

Then, call that function and terminate if necessary:

static IEnumerable<object> Iterator( ExAPI api )
{
   bool abort = false;

    for( int i = 0; !abort; ++i )
    {
        object obj;
        if( TryGetObject( api, i, out obj ) )
        {
            yield return obj;
        }
        else
        {
            abort = true;
        }
    }
}