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The Ruby Programming Language [mirror]
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Jeremy Evans 50c54d40a8
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 10:49:19 -07:00
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benchmark Evaluate multiple assignment left hand side before right hand side 2021-04-21 10:49:19 -07:00
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What's Ruby

Ruby is an interpreted object-oriented programming language often used for web development. It also offers many scripting features to process plain text and serialized files, or manage system tasks. It is simple, straightforward, and extensible.

Features of Ruby

  • Simple Syntax
  • Normal Object-oriented Features (e.g. class, method calls)
  • Advanced Object-oriented Features (e.g. mix-in, singleton-method)
  • Operator Overloading
  • Exception Handling
  • Iterators and Closures
  • Garbage Collection
  • Dynamic Loading of Object Files (on some architectures)
  • Highly Portable (works on many Unix-like/POSIX compatible platforms as well as Windows, macOS, etc.) cf. https://github.com/ruby/ruby/blob/master/doc/contributing.rdoc#label-Platform+Maintainers

How to get Ruby

For a complete list of ways to install Ruby, including using third-party tools like rvm, see:

https://www.ruby-lang.org/en/downloads/

Git

The mirror of the Ruby source tree can be checked out with the following command:

$ git clone https://github.com/ruby/ruby.git

There are some other branches under development. Try the following command to see the list of branches:

$ git ls-remote https://github.com/ruby/ruby.git

You may also want to use https://git.ruby-lang.org/ruby.git (actual master of Ruby source) if you are a committer.

Subversion

Stable branches for older Ruby versions can be checked out with also the following command:

$ svn co https://svn.ruby-lang.org/repos/ruby/branches/ruby_2_6/ ruby

Try the following command to see the list of branches:

$ svn ls https://svn.ruby-lang.org/repos/ruby/branches/

Ruby home page

https://www.ruby-lang.org/

Mailing list

There is a mailing list to discuss Ruby. To subscribe to this list, please send the following phrase:

subscribe

in the mail body (not subject) to the address ruby-talk-request@ruby-lang.org.

How to compile and install

  1. If you want to use Microsoft Visual C++ to compile Ruby, read win32/README.win32 instead of this document.

  2. Run ./autogen.sh to generate configure, when you build the source checked out from the Git repository.

  3. Run ./configure, which will generate config.h and Makefile.

    Some C compiler flags may be added by default depending on your environment. Specify optflags=.. and warnflags=.. as necessary to override them.

  4. Edit include/ruby/defines.h if you need. Usually this step will not be needed.

  5. Optional: Remove comment mark(#) before the module names from ext/Setup.

    This step is only necessary if you want to link modules statically.

    If you don't want to compile dynamic extensions (probably on architectures which do not allow dynamic loading), remove comment mark from the line "#option nodynamic" in ext/Setup.

    Usually this step will not be needed.

  6. Run make.

    • On Mac, set RUBY_CODESIGN environment variable with a signing identity. It uses the identity to sign ruby binary. See also codesign(1).
  7. Optionally, run 'make check' to check whether the compiled Ruby interpreter works well. If you see the message "check succeeded", your Ruby works as it should (hopefully).

  8. Run 'make install'.

    This command will create the following directories and install files into them.

    • ${DESTDIR}${prefix}/bin
    • ${DESTDIR}${prefix}/include/ruby-${MAJOR}.${MINOR}.${TEENY}
    • ${DESTDIR}${prefix}/include/ruby-${MAJOR}.${MINOR}.${TEENY}/${PLATFORM}
    • ${DESTDIR}${prefix}/lib
    • ${DESTDIR}${prefix}/lib/ruby
    • ${DESTDIR}${prefix}/lib/ruby/${MAJOR}.${MINOR}.${TEENY}
    • ${DESTDIR}${prefix}/lib/ruby/${MAJOR}.${MINOR}.${TEENY}/${PLATFORM}
    • ${DESTDIR}${prefix}/lib/ruby/site_ruby
    • ${DESTDIR}${prefix}/lib/ruby/site_ruby/${MAJOR}.${MINOR}.${TEENY}
    • ${DESTDIR}${prefix}/lib/ruby/site_ruby/${MAJOR}.${MINOR}.${TEENY}/${PLATFORM}
    • ${DESTDIR}${prefix}/lib/ruby/vendor_ruby
    • ${DESTDIR}${prefix}/lib/ruby/vendor_ruby/${MAJOR}.${MINOR}.${TEENY}
    • ${DESTDIR}${prefix}/lib/ruby/vendor_ruby/${MAJOR}.${MINOR}.${TEENY}/${PLATFORM}
    • ${DESTDIR}${prefix}/lib/ruby/gems/${MAJOR}.${MINOR}.${TEENY}
    • ${DESTDIR}${prefix}/share/man/man1
    • ${DESTDIR}${prefix}/share/ri/${MAJOR}.${MINOR}.${TEENY}/system

    If Ruby's API version is 'x.y.z', the ${MAJOR} is 'x', the ${MINOR} is 'y', and the ${TEENY} is 'z'.

    NOTE: teeny of the API version may be different from one of Ruby's program version

    You may have to be a super user to install Ruby.

If you fail to compile Ruby, please send the detailed error report with the error log and machine/OS type, to help others.

Some extension libraries may not get compiled because of lack of necessary external libraries and/or headers, then you will need to run 'make distclean-ext' to remove old configuration after installing them in such case.

Copying

See the file COPYING.

Feedback

Questions about the Ruby language can be asked on the Ruby-Talk mailing list (https://www.ruby-lang.org/en/community/mailing-lists) or on websites like (https://stackoverflow.com).

Bugs should be reported at https://bugs.ruby-lang.org. Read HowToReport for more information.

Contributing

See the file CONTRIBUTING.md

The Author

Ruby was originally designed and developed by Yukihiro Matsumoto (Matz) in 1995.

matz@ruby-lang.org