Re: [eigen] FFT update

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2010/1/23 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
> By the way, this "ReturnByValue::coeff() crashes by infinite
> recursion" thing is really ugly, I wonder how to fix it!!
>
> C++0x at last brings the ability to remove a base class function from
> a derived class... I wonder how to implement that idea in C++98. Is
> that enable_if?

Forget enable_if, forget C++0x, forget boost, i'm your new idol.

If we want to make sure that using ReturnByValue::coeff() generates an
error at compile time without generating an error until it's actually
used, we can define a class:

class Unusable
{
  // implement copy ctor/operator as private to disable them
  Unusable(const Unusable&) {}
  void operator=(const Unusable&) {}
};

We then let ReturnByValue::coeff() return that:

class ReturnByValue
{
....
  Unusable coeff(int, int) { return Unusable(); }
....
};

The result is that when the user does e.g.
  x = retval.coeff(i);
or
  x = retval.coeff(i) + 123;
he gets compilation errors.

Just doing
  retval.coeff(i);
doesn't give an error, but that should be optimizable as just a NOP anyway.

With this, i go to bed full^Wproud of myself.

Benoit

>
> Benoit
>
> 2010/1/23 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
>> Hi,
>>
>> Here's an example: see attached file.
>> Enjoy!!
>> Benoit
>>
>> 2010/1/22 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
>>> ok let me write an example...
>>>
>>> 2010/1/22 Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>:
>>>> On Fri, 22 Jan 2010, Benoit Jacob wrote:
>>>>
>>>>> Our "policy" is now:
>>>>> - try to return by value, optimizing with the ReturnByValue class,
>>>>> wherever possible;
>>>>> - otherwise you can just use references.
>>>>
>>>> Can somebody please explain how to use the ReturnByValue class?
>>>> Or should I just extrapolate from the source code?
>>>> I could not find any documentation.
>>>>
>>>> Jitse
>>>>
>>>>
>>>>
>>>
>>
>