Support #692
Local variables hiding out ones at top level
Description
In function definitions local variables hiding outer ones are signalled by a Warning.
At top level not. This might be confusing!
(... when someone has the bad habit of calling all variables x ;-)
/**/ Use QQ[x,y,z]; /**/ for x:=1 to 6 do print x+1 ; endfor; 234567 /**/ [ x+5 | x in 1..6]; [6, 7, 8, 9, 10, 11]
Related issues
History
#1
Updated by John Abbott almost 9 years ago
Updated by In the example given I note that x is actually a protected variable -- perhaps even more reason for a warning?
#2
Updated by John Abbott about 4 years ago
- Target version changed from CoCoA-5.?.? to CoCoA-5.4.0
I'm now quite undecided about this.
Every so often I do get a warning about one variable hiding another, but it is almost always a nuisance rather than a help. To eliminate the warning I must then change the name of a variable, but that can be "annoying".
Here is an artificial example:
define fn(L) for j:=1 to len(L) do something; endfor; j := 1; while not(IsGood(L[j]) do incr(ref j); endwhile; // now use index j ... enddefine;
#3
Updated by John Abbott over 3 years ago
- Status changed from New to In Progress
- % Done changed from 0 to 10
I think I now prefer not to issue a warning in the examples given here.
If CoCoA issues too many warnings then the user may end up simply ignoring them.
As hinted in the comment above, I might even be tempted to remove the warnings which are currently given inside a user defined function when a local variable is also used as a loop variable. Here is another example of an annoying warning:
define john(n)
L := [i in 1..n | IsPrime(i)];
i := 1;
while i <= len(L) do
if IsPrime(L[i]+2) then return i; endif;
endwhile;
return 0;
enddefine;
The main point here is that he loop variable
i in the first line of the function appears before the "scope" of the local variable i begins. However, CoCoA extends the "scope" of the local variable to the whole function... so a warning is issued.They do say that using the same variable for different purposes inside a single function is poor style... :-/
#4
Updated by John Abbott over 3 years ago
- Status changed from In Progress to Rejected
- Assignee set to John Abbott
- % Done changed from 10 to 100
- Estimated time set to 0.99 h
After a Skype discussion we have decided to leave things as they are: while not perfect (and sometimes annoying) the warnings may be a useful guide to programmers with not so much experience.