Surprising Indexed String behavior

[George Hovey-2]

/*

The following program illustrates a behavior of Indexed Strings that "surprised" me.  An indexed string IRx has the following indices set:

   ["A"], ["B"], ["A", 1], ["A", 1, 2] and ["B", 1, 2]

These elements are then displayed twice: directly, and then using a loop with the "OVER" keyword.  The surprising behavior is that the element ["B", 1, 2] is accessible in the direct display, but not when using the loop.

Obviously, the proximate cause is the failure to define indices ["B", 1], and I can see that this is not necessarily a bug.  Still it is a disturbing result and seems to deserve some insightful exegesis in NRL.

One other item.  The direct display "knows" that the value of IRx ["B", 1]="B", I guess because IRx["B"]="B" overrides the default for IRx ("?").  Again, the loop does not know.  Perhaps more could be said about this.

*/

-- Program IRx.nrx

IRx = Rexx "?"    -- indexed rexx variable

IRx["A"]    = "A"
IRx["B"]    = "B"

IRx["A", 1] = "A1"
-- don't set indices ["B", 1]

IRx["A", 1, 2] = "A12"
IRx["B", 1, 2] = "B12"
Say
Say "Directly display set values"
Say
Do
   Say '   IRx["A"] =' IRx["A"]
   Say '   IRx["B"] =' IRx["B"]
  
   Say '   IRx["A", 1] =' IRx["A", 1]
   Say '   IRx["B", 1] =' IRx["B", 1]
  
   Say '   IRx["A", 1, 2] =' IRx["A", 1, 2]
   Say '   IRx["B", 1, 2] =' IRx["B", 1, 2]
End

Say
Say "Display using the 'OVER' keyword"
Say

Loop j1 Over IRx
   Say "   IRx["j1"]="IRx[j1]
   Loop j2 Over IRx[j1]
      Say "      IRx["j1", "j2"]="IRx[j1, j2]
      Loop j3 Over IRx[j1,j2]
         Say "         IRx["j1", "j2", "j3"]="IRx[j1, j2, j3]
      End
   End
End
Say

/* Program displayed

Directly display set values

   IRx["A"] = A
   IRx["B"] = B
   IRx["A", 1] = A1
   IRx["B", 1] = B
   IRx["A", 1, 2] = A12
   IRx["B", 1, 2] = B12

Display using the 'OVER' keyword

   IRx[A]=A
      IRx[A, 1]=A1
         IRx[A, 1, 2]=A12
   IRx[B]=B
*/

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[Kermit Kiser]

I don't think this is a bug but it may need more explicit documentation of how it works.

Rexx objects are actually only indexed in a single dimension. When you use multiple indexes, you are following a "chain" of Rexx objects. Since your item ["B", 1] was never created, it does not really exist and there is no element to return for your LOOP OVER code segment.  The direct reference to it returns the default value from item ["B"]. However when you created item ["B", 1, 2], a "ghost" node for ["B", 1] was defined in the hashmap chain to set that element, hence a direct reference can locate it.

Since that behavior might surprise some, I recommend that you open a tracking issue on Kenai:

https://kenai.com/projects/netrexx

That will remind us to discuss possible solutions and documentation.

-- Kermit

On 7/15/2014 6:05 AM, George Hovey wrote:

/*

The following program illustrates a behavior of Indexed Strings that "surprised" me.  An indexed string IRx has the following indices set:

   ["A"], ["B"], ["A", 1], ["A", 1, 2] and ["B", 1, 2]

These elements are then displayed twice: directly, and then using a loop with the "OVER" keyword.  The surprising behavior is that the element ["B", 1, 2] is accessible in the direct display, but not when using the loop.

Obviously, the proximate cause is the failure to define indices ["B", 1], and I can see that this is not necessarily a bug.  Still it is a disturbing result and seems to deserve some insightful exegesis in NRL.

One other item.  The direct display "knows" that the value of IRx ["B", 1]="B", I guess because IRx["B"]="B" overrides the default for IRx ("?").  Again, the loop does not know.  Perhaps more could be said about this.

*/

-- Program IRx.nrx

IRx = Rexx "?"    -- indexed rexx variable

IRx["A"]    = "A"
IRx["B"]    = "B"

IRx["A", 1] = "A1"
-- don't set indices ["B", 1]

IRx["A", 1, 2] = "A12"
IRx["B", 1, 2] = "B12"
Say
Say "Directly display set values"
Say
Do
   Say '   IRx["A"] =' IRx["A"]
   Say '   IRx["B"] =' IRx["B"]
  
   Say '   IRx["A", 1] =' IRx["A", 1]
   Say '   IRx["B", 1] =' IRx["B", 1]
  
   Say '   IRx["A", 1, 2] =' IRx["A", 1, 2]
   Say '   IRx["B", 1, 2] =' IRx["B", 1, 2]
End

Say
Say "Display using the 'OVER' keyword"
Say

Loop j1 Over IRx
   Say "   IRx["j1"]="IRx[j1]
   Loop j2 Over IRx[j1]
      Say "      IRx["j1", "j2"]="IRx[j1, j2]
      Loop j3 Over IRx[j1,j2]
         Say "         IRx["j1", "j2", "j3"]="IRx[j1, j2, j3]
      End
   End
End
Say

/* Program displayed

Directly display set values

   IRx["A"] = A
   IRx["B"] = B
   IRx["A", 1] = A1
   IRx["B", 1] = B
   IRx["A", 1, 2] = A12
   IRx["B", 1, 2] = B12

Display using the 'OVER' keyword

   IRx[A]=A
      IRx[A, 1]=A1
         IRx[A, 1, 2]=A12
   IRx[B]=B
*/

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Online Archive : http://ibm-netrexx.215625.n3.nabble.com/