Bug #15241: net/pop fix to use mutable strings was too eager

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.5.2
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN

[eventualbuddha (Brian Donovan)]

See [[https://github.com/ruby/ruby/commit/3993fbb5f6bfdae0bce040988d7e2dd632247cdc#commitcomment-30987842|this thread on Github]]. I believe the changes made in Backport #14416 for 2.5.2 (on both trunk and 2.5.x) over-eagerly applied mutability to literal strings. In particular, the strings returned by inspect have no real need to be mutable as far as I can tell.

[eventualbuddha (Brian Donovan)]

• ruby -v changed from 2.5w to 2.5.2

[normalperson (Eric Wong)]

[e-mail] wrote:
> https://bugs.ruby-lang.org/issues/15241
> See
> [[https://github.com/ruby/ruby/commit/3993fbb5f6bfdae0bce040988d7e2dd632247cdc#commitcomment-30987842|this
> thread on Github]]. I believe the changes made in Backport
> #14416 for 2.5.2 (on both trunk and 2.5.x) over-eagerly
> applied mutability to literal strings. In particular, the
> strings returned by `inspect` have no real need to be mutable
> as far as I can tell.

We cannot make assumptions about how people use strings returned
from .inspect.  Such code exists and we should not break it:

warn(foo.inspect << " #{__FILE__}:#{__LINE__}")

Disclaimer: I do not speak for the rest of ruby-core.

This worked in 2.2 and earlier, and we should be maintaining
compatibility with such code.  If we have .inspect method
returning frozen strings, I consider it a bug.

I hate that we allocate extra objects and lose performance;
but losing compatibility and breaking existing code is worse.

[Eregon (Benoit Daloze)]

I think it's very bad style to modify the return value of #inspect, and some objects do already return frozen strings for #inspect.
So I think it would be a fair enough to change as it seems to have very low risk, i.e.,
it would only break code which is questionable in the first place (and should use + or interpolation instead).

OTOH, it's likely irrelevant for performance, and could likely be optimized if needed anyway.
So I think there is not much to gain either way, but conceptually it's wrong for user code to assume the result #inspect is always mutable.

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Rejected

I don't think that this should be considered a bug. Going from immutable to mutable should not break things, while going from mutable to immutable can. It is true that the using String#+ can decrease performance slightly, but that should not be considered a bug.