Issue #15393 has been updated by shevegen (Robert A. Heiler).


About the name - some suggestions if only to show which variants may be
better than others. :)

   frozen: true # could say "ruby, freeze as much as you possibly can!"

In other words, that setting/flag could mean that strings, hashes and arrays
are frozen (if the above is approved).

Or:

    frozen_string_array_hash_literals: true
    frozen_string_hash_array_literals: true
    frozen_three_literals: true

I am not saying any of these names are good names. Just putting them down. :)

    frozen_literals: true

I think one advantage for frozen_literals is that it is short. People could
use that in .rb files too.

Another approach could of course also be to only allow strings to be frozen
(which will become the default in ruby 3.x if I remember correctly); and not
allow a change of hash and arrays in a .rb file, but to allow it for the
suggestion above, e. g. in RubyVM.

One could also split the above up into hash and array as separate calls,
so rather than:

    RubyVM::InstructionSequence.compile(<<-eocode, __FILE__, nil, 0, frozen_string_literal: true, frozen_hash_and_array_literal: true)

to have:

    RubyVM::InstructionSequence.compile(<<-eocode, __FILE__, nil, 0, frozen_string_literal: true, frozen_hash_literal: true, frozen_array_literal: true)

I mention the last primarily because we already have frozen string literals; so for
consistency it may be useful to have it split up into hash and arrays too. If this
is too cumbersome to use three separate calls, then one could always use keys that
unify these, such as in the example given by Aaron:

    frozen_hash_and_array_literal: true

could also include Strings into it:

    frozen_string_and_hash_and_array_literal: true

It's a bit cumbersome though. Perhaps a simple variant may then be:

    frozen: true
    frozen_literal: true
    frozen_literals: true

This could then mean to "freeze all that can be frozen".

Anyway; I think the first step is to ask matz about the functionality
itself, and then see which API may be best if this is approved. 

Personally I think "frozen_literals" would be ok, even if the name
may not be 100% "perfect". Ruby is not necessarily perfect in all
names e. g. I remember a few folks thinking that the word constant 
implies "can not be changed", which may be the accurate meaning,
but from within ruby itself, I think it is perfectly fine to let 
people change constants if they want to (e. g. the philosophy of
ruby to be practical and useful).

----------------------------------------
Feature #15393: Add compilation flags to freeze Array and Hash literals
https://bugs.ruby-lang.org/issues/15393#change-75489

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Hi,

I would like to add VM compilation options to freeze array and hash literals.  For example:

~~~ ruby
frozen = RubyVM::InstructionSequence.compile(<<-eocode, __FILE__, nil, 0, frozen_string_literal: true, frozen_hash_and_array_literal: true)
  { 'a' => ['b', { 'c' => 'd' }] }
eocode
puts frozen.disasm
~~~

Output is:

~~~
$ ./ruby thing.rb
== disasm: #<ISeq:<compiled>@thing.rb:0 (0,0)-(0,34)> (catch: FALSE)
0000 putobject                    {"a"=>["b", {"c"=>"d"}]}
0002 leave
~~~

Anything nested in the hash that can't be "frozen" will cause it to not be frozen.

For example:

~~~ ruby
not_frozen = RubyVM::InstructionSequence.compile(<<-eocode, __FILE__, nil, 0, frozen_string_literal: true, frozen_hash_and_array_literal: true)
  { 'a' => some_method }
eocode
puts not_frozen.disasm
~~~

Output:

~~~
$ ./ruby thing.rb
== disasm: #<ISeq:<compiled>@thing.rb:0 (0,0)-(0,24)> (catch: FALSE)
0000 putobject                    "a"
0002 putself
0003 opt_send_without_block       <callinfo!mid:some_method, argc:0, FCALL|VCALL|ARGS_SIMPLE>, <callcache>
0006 newhash                      2
0008 leave
~~~

Eventually I would like to freeze array and hash literals in source code itself, but I think this is a good first step.

The reason I want this feature is I think we can reduce some object allocations, and once Guilds are implemented, easily create immutable data.

I've attached a patch that implements the above.

(Also I think maybe "frozen_literals" would be a better name, but I don't want to imply that numbers or booleans are frozen too)

Thanks!

---Files--------------------------------
0001-Add-compile-options-for-freezing-hash-and-array-lite.patch (6.14 KB)


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