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Creating An Array Name At Runtime?
Posted: Tue Jul 08, 2014 1:56 am
by staringfrog
Could you tell me what are the (right/slick) ways of creating array names at runtime? I but vaguely remember there are some cute operators in languages like C or PHP that turn a variable value into a new variable's name, though of course I don't expect such syntax flexibility from PB. From what I've learned up until now, this is the only way I can do this in me PB code:
Code: Select all
Macro NewDim(counter,size)
Dim MSV#counter.s(size)
MSV#counter(size)="Result"
Debug MSV#counter(size)
EndMacro
foo.i=0 : bar.i=0
NewDim(foo,bar)
Is this the only option for creating an unlimited/non-predefined number of arrays in PB? Or should I use some different logic instead?
Re: Creating An Array Name At Runtime?
Posted: Tue Jul 08, 2014 3:16 am
by Demivec
You cannot define a variable's name at runtime. The variable's name is only used at compile-time to produce the compiled code. There are some exceptions to this using the 'RunTime' keyword (the keyword exposes selected compile-time names to access via strings at runtime).
In addition to the method you showed for creating compile-time names here is a method for creating runtime names using a map:
Code: Select all
Structure MSV_Array
Array MSV.s(0)
EndStructure
NewMap MSV_Array.MSV_Array()
Procedure NewDim(counter, size)
Shared MSV_Array()
AddMapElement(MSV_Array(), "MSV" + Str(counter))
Dim MSV_Array()\MSV(size)
MSV_Array()\MSV(size)="Result"
Debug MSV_Array()\MSV(size)
EndProcedure
foo.i = 0: bar.i = 0
NewDim(foo, bar)
foo = 2: bar = 10
NewDim(foo, bar)
Debug "0 " + MSV_Array("MSV0")\MSV(0)
Debug "2 " + MSV_Array("MSV2")\MSV(10)
Debug "5 " + MSV_Array("MSV5")\MSV(0) ;doesn't exist (reference uses default declared size)
Debug "3 " + MSV_Array("MSV3")\MSV(0)
Debug "95 " + MSV_Array("MSV95")\MSV(0)
The map allows for flexible naming at runtime and reference of the array when combined with the structure that houses the array itself.
Re: Creating An Array Name At Runtime?
Posted: Tue Jul 08, 2014 3:38 pm
by staringfrog
Thank you,
Demivec, for your full explanation,
yes, I didn't think of maps as accepting concatenated array names for keys. All in all, your modification provides much more readable and flexible albeit a bit more complicated (on the face of it) solution, as well as exemplifies that basic principle behind PureBasic data manipulation (that I agree with) which states — if you want to do something really subtle with PB arrays, use arrays together with maps, and with linked-lists, and with structures. Not to mention pointers
Re: Creating An Array Name At Runtime?
Posted: Tue Jul 08, 2014 5:09 pm
by Demivec
Your welcome.
All in all, your modification provides much more readable and flexible albeit a bit more complicated (on the face of it) solution, as well as exemplifies that basic principle behind PureBasic data manipulation (that I agree with) which states — if you want to do something really subtle with PB arrays, use arrays together with maps, and with linked-lists, and with structures. Not to mention pointers
The key to it all is really the structure containing the array. Here is a slightly less complicated version using arrays of arrays. It only uses an index# instead of a custom name and would be a little simply and faster because a hash of the array's name wouldn't have to be made (for lookup in a map). It also allows the side benefit of being able to access more than one of the arrays at the same time (although this could be done with the former map example using pointers).
Code: Select all
Structure MSV_Array
Array MSV.s(0)
EndStructure
Dim MSV_Arr.MSV_Array(0)
Procedure NewDim(counter, size)
Shared MSV_Arr()
If ArraySize(MSV_Arr()) < counter
ReDim MSV_Arr.MSV_Array(counter)
EndIf
Dim MSV_Arr(counter)\MSV(size)
MSV_Arr(counter)\MSV(size)="Result"
Debug MSV_Arr(counter)\MSV(size)
EndProcedure
foo.i = 0: bar.i = 0
NewDim(foo, bar)
NewDim(2, 10)
Debug "0 " + MSV_Arr(0)\MSV(0)
Debug "2 " + MSV_Arr(2)\MSV(10) ;this will also create a default size for an array at index 1
Debug "1 " + MSV_Arr(1)\MSV(0) ;not formally declared and it's base element is still empty