[Rcpp-devel] Datetime substraction bug ?

I don't have any problem with Dirk's convention, and as Dirk said that should not create such a discussion (and it was not my intention to create one, just to point a problem I had if this can help others).

However I think that your example is designed to miss my point. My point was that the syntax for the use of operator "-" is NOT "-(c(1,3))" but "1-3" which makes the logical assertion "(1-3)>0" true.  This is not what I would call a usual convention.

Nothing more to say. Still in deep addictive love with Rcpp...

R.


----- Mail original -----
De: "Patrick Burns" <patrick at burns-stat.com>
?: rcpp-devel at lists.r-forge.r-project.org
Envoy?: Mardi 2 Avril 2013 17:34:37
Objet: Re: [Rcpp-devel] Datetime substraction bug ?

In case Dirk is feeling lonely, I'll side with him.

I think the ultimate issue is abstraction versus
application.  In a purely abstract setting, then I
agree that `-`(1, 3) should be negative.  But we
don't have a purely abstract setting.  I agree with
Dirk's New Year's/Easter example -- if the dates are
in order, then the diff should be positive to my
mind.

Note also:

  > diff(c(1, 3))

[1] 2

Pat


On 02/04/2013 15:33, Romain Francois wrote:

Le 30/03/13 00:44, Dirk Eddelbuettel a ?crit :

On 29 March 2013 at 23:37, Robin Girard wrote:
| Hi List
|
| why is it that we have in the Datetime definition
| (here
http://dirk.eddelbuettel.com/code/rcpp/html/Date_8cpp_source.html#l00271
)
|
| double operator-(const Datetime& d1, const Datetime& d2) { return
d2.m_dt - d1.m_dt; }
| bool operator<(const Datetime &d1, const Datetime& d2) { return
d1.m_dt < d2.m_dt; }
|
| I feel there is a contradiction
| substraction shoulb be d1.m_dt - d2.m_dt;  no ?

It's been a while since I wrote that and I think I followed the
difftime()
convention in R. Or maybe not.  To me d1 comes before d2 in the way the
arguments are given, so d2 is larger and I want to subtract d1 from d2.

Well. operator-(a, b) is supposed to implement a-b. See e.g. wikipedia
http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B

The current implementation does not make sense to me. So I second Robin
here.

In any event, if it bugs you greatly you are always free to write your
own
function. ;-)

Dirk

wtf. This is the same as saying 3-1 = -2

And if i follow your logic, why is the operator< implemented this way
(correctly this time).

| Robin
|
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