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Feature #15393

Add compilation flags to freeze Array and Hash literals

Added by tenderlovemaking (Aaron Patterson) over 1 year ago. Updated over 1 year ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:90375]

Description

Hi,

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

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:

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!


Related issues

Related to Ruby master - Feature #16600: Optimized opcodes for frozen arrays and hashes literalsOpenActions

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