Ruby

If you want to get a mutable string from an interpolated literal +"_#{method1}_", 2 allocation will be done instead of 1, if it weren't pointlessly frozen.

In this case a feature designed to reduce allocations is producing more allocations. Behavior that's counter-intuitive and illogical and acting counter to its intent, is not simple.

This happens to be something that can be changed without breaking anything. Can it get a second look?

If you would like the behavior changed, you should file a feature request for it, and add it to the agenda of a future developer meeting.

FWIW I'd be +1 to make interpolated Strings non-frozen.
It's BTW still the behavior in TruffleRuby to this day, since it seems to cause no incompatibility and is convenient for writing the core library with Ruby code.

Can't we just treat this as I feature request? The reasons are, it will reduce allocations, be more logical, less surprising and produce simpler code (when a mutable string is needed and you don't want extra allocations)

+1
A while ago I opened ticket #16047 about the same thing.
Seems a lot of people don't like the current behavior so much.

If you want to get a mutable string from an interpolated literal +"#{method1}", 2 allocation will be done instead of 1

Maybe the parser could understand +"#{}" and avoid that second allocation? The same way it understand "".freeze.

Because I understand the consistency argument. "All string literals are frozen" is much easier to wrap your head around than "All string literals are frozen except the ones that are interpolated".

byroot (Jean Boussier) wrote in #note-8:

Because I understand the consistency argument. "All string literals are frozen" is much easier to wrap your head around than "All string literals are frozen except the ones that are interpolated".

I'd argue "a#{2}c" is not a string literal ("a2c" is a string literal).
It's actually syntactic sugar for mutableEmptyStringOfSourceEncoding << "a" << 2.to_s << "c".
(+ .freeze the result in current semantics which feels unneeded)
Same as 42 is an integer literal, but 41 + 1 is not an integer literal.

I'd argue "a#{2}c" is not a string literal ("a2c" is a string literal).

I understand your point of view. However in my view what defines a literal, is the use of a specific syntax, so "" in this case.

Same for hashes or arrays, [1 + 2] is a literal (to me), it might not be a "static" literal, but it is a literal nonetheless.

However in my view what defines a literal, is the use of a specific syntax, so ""

There is only one reason for freezing literals, to be able to intern them and reduce allocation. In fact the feature is poorly named, after the consequence(freezing), not the cause (interning).

Freezing strings that are not interned is pointless and counterproductive (it leads to more allocation in the name of less).

A user who does not understand why literals are frozen is unlikely to even notice that interpolated ones are not. And if he does and wonders why, he will, if persistent, arrive at the reason (interning) and be better off for it. The foolish, in this case, consistency in the name of "simplicity" helps no one.

bughit (bug hit) wrote in #note-11:

However in my view what defines a literal, is the use of a specific syntax, so ""

There is only one reason for freezing literals, to be able to intern them and reduce allocation. In fact the feature is poorly named, after the consequence(freezing), not the cause (interning).

My understanding is that another reason is avoidance of alias effects. It's easy to write code that when cut down to the essential, does this:

a = b = "My string"
a.gsub!(/My/, 'Your')

and expects b to still be "My string". Freezing makes sure this throws an error.

(This is not an argument for or againts freezing interpolated strings.)

another reason is avoidance of alias effects

What you've shown is not another reason for freezing.

a = b = "My string"

both a and b refer to the same string object regardless of interning/freezing

there's no expectation that mutating it via a will not affect b

the interning scenario is:

a = "My string"
b = "My string"
a.gsub!(/My/, 'Your')

here there's an appearance of 2 string objects but when they are interned, there's only one, so mutation can not be allowed. As I said, interning is the feature, and it requires freezing.

Non-freezing interpolated strings is good thing to reduce allocations.
I think it is possible if most developers understands difference of interpolated and non-interpolated strings.

OK. Persuaded. Make them unfrozen.

Matz.

Eregon (Benoit Daloze) wrote in #note-17:

I'll try to make a PR for this change: https://github.com/ruby/ruby/pull/3488

Thanks, I've given it a try.

I found "foo#{ "foo" }" frozen because it is optimized to "foofoo" at the parser. What do you think?

$ ./miniruby --enable-frozen-string-literal -e 'p "foo#{ "foo" }".frozen?'
true

mame (Yusuke Endoh) wrote in #note-18:

I found "foo#{ "foo" }" frozen because it is optimized to "foofoo" at the parser. What do you think?

I guess that's semantically correct (besides the frozen status), since interpolation does not need to call #to_s for a String.
Since such code is very unlikely to appear in real code, I think it ultimately does not matter too much.

But if we can easily remove that optimization in the parser, I think it would be better, because this is an inconsistency (it makes it harder to reason about Ruby semantics & it breaks referential transparency) and optimizing "foo#{ "foo" }" seems to have no use in practice.
Could you point me to where the optimization is done in the parser if you found it? :)

https://github.com/nobu/ruby/tree/unfrozen-literal

I found that freezing interpolated strings are help for Ractor programming with constants.

class C
  i = 10
  STR = "foo#{i}"
end

ko1 (Koichi Sasada) wrote in #note-21:

I found that freezing interpolated strings are help for Ractor programming with constants.

Right, anything deeply frozen is helpful for Ractor.
But interpolated Strings are probably not that common.
I see an interpolated String much like an Array literals, and those are not frozen without an explicit .freeze.
Related comment: https://bugs.ruby-lang.org/issues/17100#note-23

I merged https://github.com/ruby/ruby/pull/3488 so it's in time for preview1.
@nobu (Nobuyoshi Nakada) Could you decide if you think https://github.com/nobu/ruby/tree/unfrozen-literal is worth it?