sets

[DelphiGuy]

Code: Select all

x = {a, b, c}
while y in x
    dosomething

Code: Select all

while y==a or y==b or y==c
    dosomething

i say these two code snippets are (or should be) functionally identical. yes?

[nerdzero]

On the surface, I think so. Is this some kind of trap?

[bertpritchard]

Lol. That's the same thought I had. I wondered if it was a trick question.

[Charles]

Same here. The following code works. I just used ints. Are you having problems with your own defined classes? Let us know.

"""
cobra set-in-or.cobra
"""

class P

    def main
        .one
        .two
        print 'done.'
            
    def one
        print 'one'
        a, b, c = 1, 2, 3
        x = {a, b, c}
        y = a
        trace y, x
        while y in x
            .doSomething
            if y == a, y = b
            else, y = .d
            trace y, x
        print 'done with one'

    def two
        print 'two'
        a, b, c = 1, 2, 3
        y = a
        trace y, a, b, c
        while y==a or y==b or y==c
            .doSomething
            if y == a, y = b
            else, y = .d
            trace y, a, b, c
        print 'done with two'
    
    def doSomething
        pass

    def d as int
        return 4

[DelphiGuy]

LOL! yes, i'm having trouble tracking down the apparently conflicting behavior of the two formats, but before i give the debugging effort more time (including cleaning up and presenting an actual example of the conflict -- i'm a VERY slow programmer), i just wanted to make sure it wasn't "operator error".

sorry for the misleading tone. no trick question. just "am i chasing my tail in circles simply because i am unreasonably expecting cobra to do something other than what i'm (inadvertently) explicitly asking it to do?"

thanks for the heads up.

on an entirely different topic, i'm finally about to wade into mac/monotouch, figuring that i find programming so challenging, i might as well be challenged by my true target platform (iPhone, iPod) instead of win 7.

[DelphiGuy]

Code: Select all

class P

    def main
        .three
        print 'done.'
        Console.readKey
           
    def three
      print 'three'
      a, b, c = 1, 2, 3
      x = {a, b, c}
      trace a, x
      a = 4
      trace a, x
      print 'done with three'

ok, now i get it. so assignments to variables of type "set" are by value, not by reference. i couldn't understand the wacky behavior i was getting within my "while" loop (which used the set as a looping condition). i was assigning a new value to one of the variables that had been an element in the original set assignment prior to the loop, and wrongly expecting the value of that element of the set to be updated as a result. thanks for the piece of code, which helped me learn more about how to do a simple debug like this.

[Charles]

You are basically correct, although your terminology is off.

In the .NET world, sets and other objects are assigned by reference. Only structs and primitive types (ints, bool, char, float, decimal) are assigned by value.

Sets, like lists and dictionaries, are collections. Also, they have no tie back to variables. These two sets are equivalent:

set1 = {1, 2}

x, y = 1, 2
set2 = {x, y}

assert set1 == set2  # equal because contents are the same
assert set1 is not set2  # not the same object