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# NEWS for Ruby 3.1.0
2020-02-16 15:00:34 -05:00
This document is a list of user visible feature changes
since the **3.0.0** release, except for bug fixes.
Note that each entry is kept to a minimum, see links for details.
## Language changes
Evaluate multiple assignment left hand side before right hand side In regular assignment, Ruby evaluates the left hand side before the right hand side. For example: ```ruby foo[0] = bar ``` Calls `foo`, then `bar`, then `[]=` on the result of `foo`. Previously, multiple assignment didn't work this way. If you did: ```ruby abc.def, foo[0] = bar, baz ``` Ruby would previously call `bar`, then `baz`, then `abc`, then `def=` on the result of `abc`, then `foo`, then `[]=` on the result of `foo`. This change makes multiple assignment similar to single assignment, changing the evaluation order of the above multiple assignment code to calling `abc`, then `foo`, then `bar`, then `baz`, then `def=` on the result of `abc`, then `[]=` on the result of `foo`. Implementing this is challenging with the stack-based virtual machine. We need to keep track of all of the left hand side attribute setter receivers and setter arguments, and then keep track of the stack level while handling the assignment processing, so we can issue the appropriate topn instructions to get the receiver. Here's an example of how the multiple assignment is executed, showing the stack and instructions: ``` self # putself abc # send abc, self # putself abc, foo # send abc, foo, 0 # putobject 0 abc, foo, 0, [bar, baz] # evaluate RHS abc, foo, 0, [bar, baz], baz, bar # expandarray abc, foo, 0, [bar, baz], baz, bar, abc # topn 5 abc, foo, 0, [bar, baz], baz, abc, bar # swap abc, foo, 0, [bar, baz], baz, def= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz], baz, foo # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0 # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0, baz # topn 2 abc, foo, 0, [bar, baz], baz, []= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz] # pop [bar, baz], foo, 0, [bar, baz] # setn 3 [bar, baz], foo, 0 # pop [bar, baz], foo # pop [bar, baz] # pop ``` As multiple assignment must deal with splats, post args, and any level of nesting, it gets quite a bit more complex than this in non-trivial cases. To handle this, struct masgn_state is added to keep track of the overall state of the mass assignment, which stores a linked list of struct masgn_attrasgn, one for each assigned attribute. This adds a new optimization that replaces a topn 1/pop instruction combination with a single swap instruction for multiple assignment to non-aref attributes. This new approach isn't compatible with one of the optimizations previously used, in the case where the multiple assignment return value was not needed, there was no lhs splat, and one of the left hand side used an attribute setter. This removes that optimization. Removing the optimization allowed for removing the POP_ELEMENT and adjust_stack functions. This adds a benchmark to measure how much slower multiple assignment is with the correct evaluation order. This benchmark shows: * 4-9% decrease for attribute sets * 14-23% decrease for array member sets * Basically same speed for local variable sets Importantly, it shows no significant difference between the popped (where return value of the multiple assignment is not needed) and !popped (where return value of the multiple assignment is needed) cases for attribute and array member sets. This indicates the previous optimization, which was dropped in the evaluation order fix and only affected the popped case, is not important to performance. Fixes [Bug #4443]
2021-04-21 13:49:19 -04:00
* Pin operator now takes an expression. [[Feature #17411]]
```ruby
Prime.each_cons(2).lazy.find_all{_1 in [n, ^(n + 2)]}.take(3).to_a
#=> [[3, 5], [5, 7], [11, 13]]
```
Evaluate multiple assignment left hand side before right hand side In regular assignment, Ruby evaluates the left hand side before the right hand side. For example: ```ruby foo[0] = bar ``` Calls `foo`, then `bar`, then `[]=` on the result of `foo`. Previously, multiple assignment didn't work this way. If you did: ```ruby abc.def, foo[0] = bar, baz ``` Ruby would previously call `bar`, then `baz`, then `abc`, then `def=` on the result of `abc`, then `foo`, then `[]=` on the result of `foo`. This change makes multiple assignment similar to single assignment, changing the evaluation order of the above multiple assignment code to calling `abc`, then `foo`, then `bar`, then `baz`, then `def=` on the result of `abc`, then `[]=` on the result of `foo`. Implementing this is challenging with the stack-based virtual machine. We need to keep track of all of the left hand side attribute setter receivers and setter arguments, and then keep track of the stack level while handling the assignment processing, so we can issue the appropriate topn instructions to get the receiver. Here's an example of how the multiple assignment is executed, showing the stack and instructions: ``` self # putself abc # send abc, self # putself abc, foo # send abc, foo, 0 # putobject 0 abc, foo, 0, [bar, baz] # evaluate RHS abc, foo, 0, [bar, baz], baz, bar # expandarray abc, foo, 0, [bar, baz], baz, bar, abc # topn 5 abc, foo, 0, [bar, baz], baz, abc, bar # swap abc, foo, 0, [bar, baz], baz, def= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz], baz, foo # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0 # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0, baz # topn 2 abc, foo, 0, [bar, baz], baz, []= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz] # pop [bar, baz], foo, 0, [bar, baz] # setn 3 [bar, baz], foo, 0 # pop [bar, baz], foo # pop [bar, baz] # pop ``` As multiple assignment must deal with splats, post args, and any level of nesting, it gets quite a bit more complex than this in non-trivial cases. To handle this, struct masgn_state is added to keep track of the overall state of the mass assignment, which stores a linked list of struct masgn_attrasgn, one for each assigned attribute. This adds a new optimization that replaces a topn 1/pop instruction combination with a single swap instruction for multiple assignment to non-aref attributes. This new approach isn't compatible with one of the optimizations previously used, in the case where the multiple assignment return value was not needed, there was no lhs splat, and one of the left hand side used an attribute setter. This removes that optimization. Removing the optimization allowed for removing the POP_ELEMENT and adjust_stack functions. This adds a benchmark to measure how much slower multiple assignment is with the correct evaluation order. This benchmark shows: * 4-9% decrease for attribute sets * 14-23% decrease for array member sets * Basically same speed for local variable sets Importantly, it shows no significant difference between the popped (where return value of the multiple assignment is not needed) and !popped (where return value of the multiple assignment is needed) cases for attribute and array member sets. This indicates the previous optimization, which was dropped in the evaluation order fix and only affected the popped case, is not important to performance. Fixes [Bug #4443]
2021-04-21 13:49:19 -04:00
* Multiple assignment evaluation order has been made consistent with
single assignment evaluation order. With single assignment, Ruby
uses a left-to-right evaluation order. With this code:
```ruby
foo[0] = bar
```
The following evaluation order is used:
1. `foo`
2. `bar`
3. `[]=` called on the result of `foo`
In Ruby before 3.1.0, multiple assignment did not follow this
evaluation order. With this code:
```ruby
foo[0], bar.baz = a, b
```
Versions of Ruby before 3.1.0 would evaluate in the following
order
1. `a`
2. `b`
3. `foo`
4. `[]=` called on the result of `foo`
5. `bar`
6. `baz=` called on the result of `bar`
Starting in Ruby 3.1.0, evaluation order is now consistent with
single assignment, with the left hand side being evaluated before
the right hand side:
1. `foo`
2. `bar`
3. `a`
4. `b`
5. `[]=` called on the result of `foo`
6. `baz=` called on the result of `bar`
[[Bug #4443]]
## Command line options
## Core classes updates
Outstanding ones only.
2021-04-16 03:12:10 -04:00
* Array
* Array#intersect? is added. [[Feature #15198]]
2021-01-02 02:42:45 -05:00
* Enumerable
* Enumerable#compact is added. [[Feature #17312]]
* Enumerable#tally now accepts an optional hash to count. [[Feature #17744]]
2021-01-02 02:42:45 -05:00
* Enumerator::Lazy
* Enumerator::Lazy#compact is added. [[Feature #17312]]
2021-03-15 07:05:03 -04:00
* File
* File.dirname now accepts an optional argument for the level to
strip path components. [[Feature #12194]]
* Module
* Module#prepend now modifies the ancestor chain if the receiver
already includes the argument. Module#prepend still does not
modify the ancestor chain if the receiver has already prepended
the argument. [[Bug #17423]]
* Struct
* Passing only keyword arguments to Struct#initialize is warned.
You need to use a Hash literal to set a Hash to a first member.
[[Feature #16806]]
* Queue
* Queue#initialize now accepts an Enumerable of initial values.
[[Feature #17327]]
* Thread
* Thread#native_thread_id is added. [[Feature #17853]]
* Thread::Backtrace
* Thread::Backtrace.limit, which returns the value to limit backtrace
length set by `--backtracse-limit` command line option, is added.
[[Feature #17479]]
2021-02-16 04:12:47 -05:00
* $LOAD_PATH
* $LOAD_PATH.resolve_feature_path does not raise. [[Feature #16043]]
## Stdlib updates
Outstanding ones only.
## Compatibility issues
Excluding feature bug fixes.
## Stdlib compatibility issues
2020-06-18 08:11:19 -04:00
2021-01-21 01:02:24 -05:00
* `ERB#initialize` warns `safe_level` and later arguments even without -w.
[[Feature #14256]]
## C API updates
## Implementation improvements
### JIT
* `RubyVM::MJIT` is renamed to `RubyVM::JIT`.
2020-11-10 12:15:57 -05:00
## Static analysis
2020-10-20 00:16:19 -04:00
### RBS
2020-09-25 04:08:39 -04:00
2020-10-20 00:16:19 -04:00
### TypeProf
## Miscellaneous changes
2021-01-02 02:42:45 -05:00
* lib/objspace/trace.rb is added, which is a tool for tracing the object
allocation. Just by requiring this file, tracing is started *immediately*.
Just by `Kernel#p`, you can investigate where an object was created.
Note that just requiring this file brings a large performance overhead.
This is only for debugging purpose. Do not use this in production.
[Feature #17762]
2021-01-02 02:42:45 -05:00
Evaluate multiple assignment left hand side before right hand side In regular assignment, Ruby evaluates the left hand side before the right hand side. For example: ```ruby foo[0] = bar ``` Calls `foo`, then `bar`, then `[]=` on the result of `foo`. Previously, multiple assignment didn't work this way. If you did: ```ruby abc.def, foo[0] = bar, baz ``` Ruby would previously call `bar`, then `baz`, then `abc`, then `def=` on the result of `abc`, then `foo`, then `[]=` on the result of `foo`. This change makes multiple assignment similar to single assignment, changing the evaluation order of the above multiple assignment code to calling `abc`, then `foo`, then `bar`, then `baz`, then `def=` on the result of `abc`, then `[]=` on the result of `foo`. Implementing this is challenging with the stack-based virtual machine. We need to keep track of all of the left hand side attribute setter receivers and setter arguments, and then keep track of the stack level while handling the assignment processing, so we can issue the appropriate topn instructions to get the receiver. Here's an example of how the multiple assignment is executed, showing the stack and instructions: ``` self # putself abc # send abc, self # putself abc, foo # send abc, foo, 0 # putobject 0 abc, foo, 0, [bar, baz] # evaluate RHS abc, foo, 0, [bar, baz], baz, bar # expandarray abc, foo, 0, [bar, baz], baz, bar, abc # topn 5 abc, foo, 0, [bar, baz], baz, abc, bar # swap abc, foo, 0, [bar, baz], baz, def= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz], baz, foo # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0 # topn 3 abc, foo, 0, [bar, baz], baz, foo, 0, baz # topn 2 abc, foo, 0, [bar, baz], baz, []= # send abc, foo, 0, [bar, baz], baz # pop abc, foo, 0, [bar, baz] # pop [bar, baz], foo, 0, [bar, baz] # setn 3 [bar, baz], foo, 0 # pop [bar, baz], foo # pop [bar, baz] # pop ``` As multiple assignment must deal with splats, post args, and any level of nesting, it gets quite a bit more complex than this in non-trivial cases. To handle this, struct masgn_state is added to keep track of the overall state of the mass assignment, which stores a linked list of struct masgn_attrasgn, one for each assigned attribute. This adds a new optimization that replaces a topn 1/pop instruction combination with a single swap instruction for multiple assignment to non-aref attributes. This new approach isn't compatible with one of the optimizations previously used, in the case where the multiple assignment return value was not needed, there was no lhs splat, and one of the left hand side used an attribute setter. This removes that optimization. Removing the optimization allowed for removing the POP_ELEMENT and adjust_stack functions. This adds a benchmark to measure how much slower multiple assignment is with the correct evaluation order. This benchmark shows: * 4-9% decrease for attribute sets * 14-23% decrease for array member sets * Basically same speed for local variable sets Importantly, it shows no significant difference between the popped (where return value of the multiple assignment is not needed) and !popped (where return value of the multiple assignment is needed) cases for attribute and array member sets. This indicates the previous optimization, which was dropped in the evaluation order fix and only affected the popped case, is not important to performance. Fixes [Bug #4443]
2021-04-21 13:49:19 -04:00
[Bug #4443]: https://bugs.ruby-lang.org/issues/4443
2021-03-16 01:07:27 -04:00
[Feature #12194]: https://bugs.ruby-lang.org/issues/12194
2021-01-21 01:02:24 -05:00
[Feature #14256]: https://bugs.ruby-lang.org/issues/14256
2021-04-16 03:12:10 -04:00
[Feature #15198]: https://bugs.ruby-lang.org/issues/15198
2021-02-16 04:12:47 -05:00
[Feature #16043]: https://bugs.ruby-lang.org/issues/16043
[Feature #16806]: https://bugs.ruby-lang.org/issues/16806
2021-01-02 02:42:45 -05:00
[Feature #17312]: https://bugs.ruby-lang.org/issues/17312
[Feature #17327]: https://bugs.ruby-lang.org/issues/17327
[Feature #17411]: https://bugs.ruby-lang.org/issues/17411
[Bug #17423]: https://bugs.ruby-lang.org/issues/17423
[Feature #17479]: https://bugs.ruby-lang.org/issues/17479
[Feature #17744]: https://bugs.ruby-lang.org/issues/17744
[Feature #17762]: https://bugs.ruby-lang.org/issues/17762