Why people dislike global variables so much while I find them so convenient?
smarksc at gmail.com
Wed Jan 26 11:52:13 UTC 2022
On Tuesday, 25 January 2022 at 09:53:25 UTC, rempas wrote:
> It is known that people dislike global variables and the reason
> is that they make the code harder to debug. In my experience
> tho, it is the exact opposite. When I have a variable that I
> must pass down to 5-6 functions, I find it much easier to make
> it global rather than having it been passed in all the
> functions that need it. This practice also makes my function
> signatures looking much cleaner. Yeah, one variable will not
> make a difference but in my project, I have about 2-3 variables
> that need to be passed down to a lot of functions so I only
> think that it makes sense to use them as globals. Another
> problem is the case that I'll introduce a new variable that
> needs to also be passed in most of my functions. What happens
> then? Let's say I will have 20 functions at the time. I have to
> change both the function signature and all the other places in
> code that call this function. The latter can be easily done
> with a quick "search and replace" in my text editor but still,
> it's a tedious thing to do.
> So can someone make examples about how global variables can
> mess me up. I know that probably everyone here has more
> personal experience than me so I really want to learn why
> global variables are considered so harmful.
Some examples of global variables that are frequently used:
1) C has an implicit global variable in all programs - errno.
2) If you are writing `asm` blocks (in C or D), then the
processor's flags and registers are obviously global variables
that can affect the function's behavior. At least in D the
compiler will complain if a function is marked `pure` but has an
inner `asm` block; the block has to be annotated explicitly with
3) The language runtime might also be considered as one giant
global variable. As an example, a function may return
successfully on one invocation and fail on another despite being
pure and being invoked with the same parameters, just because a
memory allocation has failed. Potentially, you could even catch
and handle OurOfMemoryErrors (something which you aren't supposed
to do, I think) and change function behavior based on that.
However, if I'm not mistaken, any issues related to memory
allocation aren't typically considered a part of the function's
"contract"; otherwise, `pure` would only be possible if `@nogc`
is also present.
More information about the Digitalmars-d