LiveCode Forums.

on mouseUp
   put random(5) into theTest
   if theTest = 1 then
      put "1" && theTest
   else if theTest = 2 then
      put "2" && theTest
   else if theTest = 3 then
      put "3" && theTest
   else if theTest = 4 then
      put "4" && thetest
   else 
      put "5" && theTest
   end if
end mouseUp 

ukimiku wrote:Real-world application are typically specialized sorting routines where elements get "swapped" (the contents of a becomes the contents of b and vice versa, but you cannot write someting like

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put a into b
put b into a

since as soon as the interpreter executes the first line, the original contents of b is overwritten. The typical solution is to use a temporary variable to hold one of the contents before the swap takes place, e.g.

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put a into temp
put b into a
put temp into b

which is needlessly cumbersome. How about only writing

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swap a, b

and you're done.

In my case, I wrote an implementation of the Blowfish algorithm. In it, many contents exchanges take place, and the above method (which is called very often, so it takes up a significant amount of time, too) makes the code not only slower and more cumbersome, but also harder to read than just

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swap a, b

Other languages have it too. Programming without SWAPI find equally unnverving as programming nested conditionals without ELSEIF.

Hoping to shed some light on the swappin' business...

Regards,

local tA,tB
on mouseUp
   put 4 into tA
   put 5 into tB
   swap tA,tB
   put tA && tB
end mouseUp

on swap theA,theB
   put theA into tB
   put theB into tA
end swap

FourthWorld wrote:

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on swap @pA, @pB
  get pA
  put pB into pA
  put it into pB
end swap

sturgis wrote:Or something like this? Yours is more generic though, so I think it would be the way to go.

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local tA,tB
on mouseUp
   put 4 into tA
   put 5 into tB
   swap tA,tB
   put tA && tB
end mouseUp

on swap theA,theB
   put theA into tB
   put theB into tA
end swap

FourthWorld wrote:

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on swap @pA, @pB
  get pA
  put pB into pA
  put it into pB
end swap

ukimiku wrote:Could you please explain to me the difference between a handler that starts with "on" and a "command" construct?

In my mental model of Runtime, if your implementation of SWAP was used in a stack, a message would be added to the pending messages and then processed by the "on swap" handler. Is that correct? If so, would it be much slower than using a "command swap" construct?

Of course, one canwrite such a handler that references object pointers (I find your use of "it" pretty elegant), and I could have written something alike myself, but an in-built SWAP would still be my preference, if only for reasons of execution speed. Also, I wouldn't have to remind myself for each project to copy the SWAP code into my stack.

ukimiku wrote:while recognizing that "on" handlers do not process pending messages as sent with the "SEND IN..." (time) command.

The "pending messages" is a queue for message sent with the "send in <time>" command, so not really the best descriptor here.

a message would be added to the pending messages and then processed by the "on swap" handler.

on myHandler
   answer "This dialog was brought to you through processing a send in time construct"
end myHandler

on mouseUp
   send "myHandler" to this stack in 2000 milliseconds
end mouseUp

on swap @pA, @pB
get pA
put pB into pA
put it into pB
end swap

private command swap @pA, @pB
  get pA
  put pB into pA
  put it into pB
end swap