With immutable string literals not being the default in Ruby 3, does FrozenStringLiteralComment still make sense by default? Issue #7197 rubocop rubocop

In fact, Ruby 2.3 will hold a unique instance for each string literal value used in the program. This means that ‘a’ and ‘a’ references the same object. I’m a supporter of the idea of making strings frozen by default. Maybe some syntax for unfrozen strings like ‘unfrozen’u might be a good idea rather than using dup, but I’m not really worried about this. I’m no benchmarking expert, but some quick tests locally have suggested that using frozen string literals does make code using a lot of literals a bit faster. The next morning in fired up Skylight to check the response times from the API.

Adds an offense on the specified range Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense. Returns true if the cop name or the cop namespace matches any How the web works Learn web development MDN of the given names. List of cops that should not try to autocorrect at the same time as this cop. Note that String.new with no argument returns an ASCII-8BIT string. The +’abcd’ syntax is new, can’t recall which versions it works with.

In the next section let’s take a look how this impacts on performance. It is my understanding that freeze allows Ruby to lock a String to the original text in the source code instead of creating a separate buffer as needed for a mutable object. Less experienced developers, or developers without Ruby experience, could accidentally think the string is passed as a value, not a reference. I guess the interaction between the “false” state and the current runtime default is what has me confused. I REALLY like the idea but I am sure introducing this could cause HUGE compatibility issue, even bigger than Ruby 1.9. So I officially abandon making frozen-string-literals default .

ruby frozen string literal

What about the benefit of making code easier to reason about by preventing accidental modification? Well, that benefit is already there, you just need to use it. You can call ‘freeze’ on any object and it will prevent modification.

What does using – on a String do?

In this mode, all values assigned to constants are deeply copied and made shareable. Another way to get these warnings to show is by running Ruby with warnings (ruby -w). Using a directive to set this false will prevent these warnings to show. Top-level magic comments must appear in the first comment section of a file. The term ‘frozen’ is Ruby’s way of saying immutable, which is a technical way of saying something cannot be changed. A frozen object in Ruby cannot be modified in any way – if a modification is attempted, an exception will be raised.

  • The returned String will be deduplicated as long as it does not have any instance variables set on it.
  • Maybe I was seeing the effects of cold cache calls and things would improve overnight.
  • It would be better if it could specify finer-grained range than a whole file, but I have no strong objection.
  • Any others have more information to share, please reach out.

For example, the following code could be used to create a string containing a greeting, and then to modify the greeting to make it more personal if a name is available. But, if you woke up today feeling like a kamikaze, enable frozen strings for the whole project and prepare yourself for some serious bug hunting. So, to enable string immutability for a project add the following flag when running your app.

What are Frozen Objects?

Nothing blocks the second thread from changing account.type between the comparisons made on the first one, resulting in an erroneous behavior, as no block in the if is run. As this feature is currently under development, it may suffer some changes prior to Ruby 2.3 release. You are commenting using your WordPress.com account. Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.

First, it’s important to note that this change is just the first step towards all string literals becoming immutable in Ruby 3. String literals are simply strings that are created using Ruby’s built-in string syntax. This includes those created using double quotes (“), single quotes (‘), or the special forms %Q and %q. Traditionally, these forms have all created strings that can be modified.

ruby frozen string literal

If the change is more of an issue than we think, it just means we need more releases of “on-by-default warning” before we can turn it into a mandatory error. Once we learn more about the kinds of problems that end up existing, there may be other things we can do to help with the transition that target those use-cases directly. In Ruby, whenever you have a statement defining a string as a literal, it’s a new object, with its own space in memory. “a” in one line of your code and “a” in another have the same contents, but are separate. And if those statements are called more than once, then every time they’re called, new strings are allocated in memory.

Last week I removed all those calls and added a frozen_string_literal comment to all Ruby files. If you aren’t using it from a constant, but instead just have a string literal somewhere in your code, that allocation cost can add up. The performance difference is real, but comes from places like Rails not from users’ applications. Then it actually makes a lot of sense to postpone frozen strings by default. This was mentioned as part of the general discussion on making string literals immutable, but not in much detail. I suggest that you propose this as a new feature, with some good use cases, if you really are interested.

That’s the only way to keep backwards compatibility, right? Ruby might introduce some other method to get the information whether the string is still in the default initial frozen state though… One possible option would be to have “” be a mutable string, and ” be an immutable string. It doesn’t make sense to have “” strings be immutable How To Use GitHub GitHub Tutorial For Beginners if they contain interpolation, since they can’t be deduped, and ” strings can’t contain interpolation. Beyond the actual usage changes, it’s probably worth adding in the pragma comment across all of your files. That may initially seem like hard work, but you can enforce this via RuboCop, and add them to existing projects with pragmater.

Since we wrote this post –enable-frozen-string-literal-debug has been renamed and its behavior has changed. First, we had to enabled it to know where string literals were being created. On Feature #11725 implementation, the original flag was renamed to –debug-frozen-string-literal. Furthermore, if we try to mutate a statically created string literal, the error message will show by default where the string was created.

::RuboCop::Cop::TargetRubyVersion – Extended

Another way would be to run the test suites of a set of gems and see how much breaks with –enable-frozen-string-literal, including gems not using the pragma. Performance should indeed be a concern in my opinion. Just because there are other faster languages it doesn’t mean performance should not be a priority for Ruby.

String literal world discussed on [Feature #11473]. The benefit of this is that you can then rely on certain objects being consistent in their value, no matter where they’re used and what other parts of code may try to do. This means fewer assumptions in your code, and that is a Good Thing. One caveat to note with String.new is that if you call it without any arguments, you do get an empty string, but it will always have an encoding of ASCII-8BIT.

ruby frozen string literal

‘a’ the interpreter creates two objects with the value ‘a’, hence equal? With immutable strings this is no longer true, in this case the interpreter will use a reference to the same object, then as each reference points to the same object equal? As it goes with most updates, there will be some short term pain as Ruby changes to make string literals immutable by default. The good news is that it will happen gradually, and it won’t be difficult to detect and fix existing code that’s affected by this change. In return, we’re going to get a version of Ruby that uses less memory and thus runs a bit quicker. Given the low overhead of having to call ‘dup’ when we want an unfrozen string, this is certainly a tradeoff worth making.

::RuboCop::Cop::AutocorrectLogic – Included

If an argument is passed, the new string will respect the encoding of the first argument – which is likely to be Ruby’s default of UTF-8. Allocating just a single object for both ‘a’ and ‘b’ reduces the amount of memory used and this, in turn, reduces pressure on the garbage collector. Matz (Ruby’s creator) decided to make all String literals frozen by default.

To me, it also looks less ugly than a magic comment. To prevent this type of bug, why is it sufficient to freeze only literals? String#+ also must return The 11 Best Free Wireframe Tools For UX UI Designers a frozen String, I think. This issue tries to match performance and usability . Why do matz and akr want to make String literals immutable, at first?

This mode is “experimental” and has not been discussed thoroughly. This will be revisited before Ruby 3.1 to either allow ‘copy` or to instead remove this mode. It must appear in the first comment section of a file. This process cannot be reversed – once an object is frozen in Ruby, it will remain frozen. The comment must be on the first line of the file.

Sign up for a free GitHub account to open an issue and contact its maintainers and the community. As a person who is responsible managing for many Ruby-based enterprise products, I really care about the compatibility. It was a nightmare to migrate our 1.8.7 codes to 1.9, because of many small incompatiblity in the release.

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