Re: scope of variables
- Posted by jeremy (admin) Dec 31, 2010
- 2629 views
here an example, an editor as a text buffer with cursor position referenced by 2 top level variables bcol and bline and there is a procedure that modify the content of that buffer but must leave cursor position unchanged at exit. all the code elsewhere use bcol and bline to access character in buffer. It make sense to use local variables of same name inside that procedure
sequence buffer -- text buffer sequence bcol -- cursor column sequence bline -- cursro line --insert text at current cursor position and leave cursor where it is. procedure insert_text(sequence text) integer bcol=bcol -- local copy integer bline=bline -- local copy --- code here end procedure -- at exit bcol and bline are preserved without need to restore from a temporary storage
That's bad practice. You know there is a global (file level) bcol, bline. Now imaging scrolling from the bottom of your file up browsing code trying to figure out why your bcol and bline variables are getting out of sync and you see the bottom end of your routine:
bcol += 10 bline+= 10 set_line("Hello, World!") end procedure
What will you think? You don't even know what method you are in at this point. Now, imagine if you would have named the variables to their real meaning, not simply shadowed a well used, well known name (why else would it be at the file level?):
local_bcol += 10 local_bline+= 10 set_line("Hello, World!") end procedure
Now what do you think? You keep on scanning looking for why your bcol and bline variables are getting screwed up.
Jeremy
