public bool MoveNext()
{
switch (state)
{
case EnumeratorState.Enumerating:
if (++sourceIndex >= end)
{
state = EnumeratorState.Complete;
return(false);
}
var enumerable = selector.Invoke(source[sourceIndex]);
subEnumerator = enumerable.GetEnumerator();
state = EnumeratorState.EnumeratingSub;
goto case EnumeratorState.EnumeratingSub;
case EnumeratorState.EnumeratingSub:
if (!subEnumerator.MoveNext())
{
state = EnumeratorState.Enumerating;
goto case EnumeratorState.Enumerating;
}
return(true);
default:
return(false);
}
}
public bool MoveNext()
{
if (first)
{
first = false;
while (enumerator.MoveNext())
{
sub = mapper(enumerator.Current).GetEnumerator();
if (sub.MoveNext())
{
return(true);
}
}
return(false);
}
else
{
if (!sub.MoveNext())
{
while (enumerator.MoveNext())
{
sub = mapper(enumerator.Current).GetEnumerator();
if (sub.MoveNext())
{
return(true);
}
}
return(false);
}
else
{
return(true);
}
}
}