9 ms·

I don't think this is the right way to think about it. The ending "state" might be the same, but the output of the first logout operation would be "change of st

by firat 14y ago

I don't think this is the right way to think about it. The ending "state" might be the same, but the output of the first logout operation would be "change of state: logged in -> logged out". In the second case, however, it would be "no change in state". It does different things under different circumstances.

kilburn 14y ago
From the Wikipedia article on Idempotence [1]: Similarly, changing a customer's address is typically idempotent, because the final address will be the same no matter how many times it is submitted. So, even if in one case there's an internal state change (going from an old address to a new one) whereas in the other there is not (going from the new address to the new one again), it is commonly considered idempotent because the end result is the same. [1] http://en.wikipedia.org/wiki/Idempotence#Computer_science_meaning http://en.wikipedia.org/wiki/Idempotence#Computer_science_me...
- firat 14y ago
  Okay, I understand that the formal definition of "idempotent" is different than what the author means. What is the correct term to use in this case? Edit: Next paragraph says: This is a very useful property in many situations, as it means that an operation can be repeated or retried as often as necessary without causing unintended effects. With non-idempotent operations, the algorithm may have to keep track of whether the operation was already performed or not. "A change in state" would be an unintended effect I think.
  - saurik 14y ago
    I think the best "term" you can use here is "side effect free". I almost wanted to say "pure" would work, but there is no real requirement that GET always return the same thing: it just needs to not change the state of the server in a way that a later GET could detect (although, honestly, you really only practically care about "find bothersome", and if there is a term for "bothersome side effect free" it would probably be from medicine and not computer science).
wtetzner 14y ago
"Idempotence is the property of certain operations in mathematics and computer science, that they can be applied multiple times without changing the result beyond the initial application."[1] [1] https://en.wikipedia.org/wiki/Idempotence https://en.wikipedia.org/wiki/Idempotence
- firat 14y ago
  What is the definition of "result". My point is that result in this case is a "change of state" vs "no change in state".
  - rhizome 14y ago
    the result of multiple log out attempts will be "attemptor will be logged out."
ajanuary 14y ago
"Methods can also have the property of "idempotence" in that ... the side-effects of N > 0 identical requests is the same as for a single request." [1] The HTTP spec clearly talks in terms of the effect of sequences of repeated operations, not in terms of the results of individual operations. The side effects of a single logout are the same as for 6 - you are logged out and whatever logout triggers exist are executed once. [1] http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2 http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1...

by firat 14y ago

kilburn 14y ago

From the Wikipedia article on Idempotence [1]: Similarly, changing a customer's address is typically idempotent, because the final address will be the same no matter how many times it is submitted. So, even if in one case there's an internal state change (going from an old address to a new one) whereas in the other there is not (going from the new address to the new one again), it is commonly considered idempotent because the end result is the same. [1] http://en.wikipedia.org/wiki/Idempotence#Computer_science_meaning http://en.wikipedia.org/wiki/Idempotence#Computer_science_me...

firat 14y ago
Okay, I understand that the formal definition of "idempotent" is different than what the author means. What is the correct term to use in this case? Edit: Next paragraph says: This is a very useful property in many situations, as it means that an operation can be repeated or retried as often as necessary without causing unintended effects. With non-idempotent operations, the algorithm may have to keep track of whether the operation was already performed or not. "A change in state" would be an unintended effect I think.
- saurik 14y ago
  I think the best "term" you can use here is "side effect free". I almost wanted to say "pure" would work, but there is no real requirement that GET always return the same thing: it just needs to not change the state of the server in a way that a later GET could detect (although, honestly, you really only practically care about "find bothersome", and if there is a term for "bothersome side effect free" it would probably be from medicine and not computer science).

wtetzner 14y ago

"Idempotence is the property of certain operations in mathematics and computer science, that they can be applied multiple times without changing the result beyond the initial application."[1] [1] https://en.wikipedia.org/wiki/Idempotence https://en.wikipedia.org/wiki/Idempotence

firat 14y ago
What is the definition of "result". My point is that result in this case is a "change of state" vs "no change in state".
- rhizome 14y ago
  the result of multiple log out attempts will be "attemptor will be logged out."

ajanuary 14y ago

"Methods can also have the property of "idempotence" in that ... the side-effects of N > 0 identical requests is the same as for a single request." [1] The HTTP spec clearly talks in terms of the effect of sequences of repeated operations, not in terms of the results of individual operations. The side effects of a single logout are the same as for 6 - you are logged out and whatever logout triggers exist are executed once. [1] http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2 http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1...