[erlang-questions] Strings - deprecated functions

[Loïc Hoguin]

On 11/24/2017 03:07 PM, Eric des Courtis wrote:
>  From my perspective, we want the following things:
> 
>   * The libraries to stay simple, small and clean (that means throwing
>     away things)
>   * Our old code to continue to work without modifications (that means
>     having a mechanism for compiling old code targetting new versions of
>     Erlang)

That can work in many cases but not in the general case. This only works 
for a specific set of changes where an equivalent still exists in the 
code base.

For example removing ciphers or hashes in crypto requires human 
intervention on every code bases that require them.

Another issue comes from old code requiring syntax or VM features that 
have been removed.

Then you have issues where it is technically still possible to do the 
old functionality, but the performance or memory aspects are not equivalent.

>   * To mix old and new Erlang code together

If it's maintained, no problem. If not, even if it compiles and runs you 
should probably make sure to have a good set of tests to know it still 
works as intended.

You'll want to do this even if OTP team go out of their way to make sure 
everything stays compatible forever.

> I see no reason why we can't have both. What I am not okay with is:
> 
>   * Endlessly growing libraries of functions that are there for legacy
>     reasons (wasting space and confusing new developers)
>   * Fixing libraries over and over again because something got marked
>     deprecated
> 
> So how do we get both?

You don't.

In fact your second point is incorrect: there's absolutely no reason to 
fix a library because something got marked deprecated.

Zero.

Developers should not "fix" libraries when something gets marked 
deprecated. Developers should *take notice* that something has been 
deprecated.

There's nothing to fix to begin with! Check your OCD levels and stop 
trying to get rid of all the deprecation warnings with obscure parse 
transforms or version-specific defines...

The time to fix comes when the feature gets *removed* or is rendered 
*incompatible*. (Or soon before that actually happens, anyway.)

As far as the string module is concerned, there's absolutely no need to 
spend efforts to make your code run for both the old and the new string 
module because the functions will not be removed for a very long time. 
And until they are, chances are you will stop supporting OTP versions 
before the new functions were introduced. You can do the changes THEN.

I am baffled every time someone opens a ticket telling me that I have 
deprecation warnings. I know! But they're harmless and the code works on 
all supported versions, so why would I spend efforts to remove it?

Your question can be reframed to be about an endlessly growing library + 
having to fix libraries when things get removed, which is more of a 
choice, you can't really have both. Either you have an endlessly growing 
library, or you remove functions and fix libraries (manually or otherwise).

-- 
Loïc Hoguin
https://ninenines.eu