CopyVar

[webmasterpdx]

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

[Joe Horn]

(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.

[ji3m]

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.

[webmasterpdx]

Thank you. Now I understand what they meant.
-Donald

[Tim Wessman]

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.