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+--- Thread: CopyVar (/thread-9019.html)
CopyVar - webmasterpdx - 09-09-2017 11:58 AM
Can anyone explain the difference between these 2 lines....in terms of what happens?
A:=B;
CopyVar(A,B);
The docs say the second line copys the storage area that B holds into A's storage area. I see no difference between that an A:=B;.....
Alternatively, give me an example where they would not be the same...
Ultimately, what I'm trying to figure out is defined in this post...
http://www.hpmuseum.org/forum/thread-9018.html
....but nobody's answered it yet...
Thx
-Donald
RE: CopyVar - Joe Horn - 09-09-2017 01:39 PM
(09-09-2017 11:58 AM)webmasterpdx Wrote: Can anyone explain the difference between these 2 lines....in terms of what happens?
A:=B;
CopyVar(A,B);
The docs say the second line copys the storage area that B holds into A's storage area. I see no difference between that an A:=B;.....
Alternatively, give me an example where they would not be the same...
The difference is that CopyVar doesn't evaluate the source variable. Here's a CAS example:
aa:='1+2' <-- this stores the algebraic expression '1+2' into aa.
bb:=aa <-- this stores the evaluated result, 3, into bb.
CopyVar(aa,cc) <-- this stores the unevaluated expression '1+2' into cc.
RE: CopyVar - ji3m - 09-09-2017 03:01 PM
This behaviour is actually quite insane. Is it xcas or just fancy thinking. It make assignment equivalentto eval. No language I know does this. It make programming a nightmare. Sorry but it's crazy stuff.
A:=B is not the same as evaluating argument in a function call.
RE: CopyVar - webmasterpdx - 09-09-2017 10:04 PM
Thank you. Now I understand what they meant.
-Donald
RE: CopyVar - Tim Wessman - 09-11-2017 03:12 PM
You are looking at this from a "programming language" perspective. However, neither the HP language nor the CAS is really a "programming language" but rather a math language to represent mathematics.
Most math languages and numerical systems do behave this way and you prevent evaluation through use of other functions, quoting arguments, etc.