From: tenderlove@... Date: 2019-01-15T00:15:59+00:00 Subject: [ruby-core:91092] [Ruby trunk Feature#15393] Add compilation flags to freeze Array and Hash literals Issue #15393 has been updated by tenderlovemaking (Aaron Patterson). Eregon (Benoit Daloze) wrote: > tenderlovemaking (Aaron Patterson) wrote: > > I thought about doing this with ".freeze", introducing a special instruction the same way we do for the `"string".freeze` optimization, but dealing with deoptization in the case someone monkey patches the method seems like a pain. > > I think it might semantically make some sense to ignore monkey-patching of `.freeze` (and `.deep_freeze`) for calls on literals, which would then avoid needing deoptimization for this (although deoptimization would be a flag check + the current logic as fallback, it doesn't seem so bad). > It's somewhat similar to String literals not calling String#initialize for instance (same for Array, Hash). > And it's probably a bad idea to override #freeze in the hope it would be used on frozen literals anyway, as of course this would only work if the monkey-patch is reliably loaded before everything else. > > Another issue is it's quite ugly to opt out of frozen array/hash literals, if a mutable copy is wanted: > > ```ruby > # frozen_hash_and_array_literal: true > my_mutable_data = { 'a' => ['b', { 'c' => 'd' }.dup].dup }.dup > ``` > > That's why I think `deep_freeze` would better express the intent in some cases, and be finer-grained: > > ```ruby > MY_CONSTANT = { 'a' => ['b', { 'c' => 'd' }] }.deep_freeze > my_mutable_data = { 'a' => ['b', { 'c' => 'd' }] } > > { :defaults => 'thing' }.deep_freeze.merge(some_hash) > ``` Yes, I totally agree. I think `deep_freeze` is going to be necessary for adoption of Guilds, and the code I'm proposing in this patch would be an optimization of the `deep_freeze` call on a literal. > and this would work regardless of what is the value to freeze (but only avoid allocations if it's all literals, otherwise a constant must be used). > > Furthermore, frozen literals don't allow composition or extraction in different constants: > ```ruby > # frozen_hash_and_array_literal: true > MY_KEY = 'a' > MY_CONSTANT = { MY_KEY => ['b', { 'c' => 'd' }] } # Not frozen, and breaks referential transparency > > MY_CONSTANT = { MY_KEY => ['b', { 'c' => 'd' }] }.deep_freeze # Works > ``` > > OTOH, "string".freeze has shown the magic comment is much nicer in many cases than adding "string".freeze in many places (at the price of making a mutable String not so nice, but those seem rarer). > It would be interesting to get an idea of what's a typical ratio of immutable/mutable Array and Hash literals, and what converting a codebase to use frozen Array/Hash literals would look like. Right. I'm not proposing adding the magic comment at all, just adding a parameter to the ISeq constructor that will allow you to "deep freeze" literals in the code passed to ISeq#new. ---------------------------------------- Feature #15393: Add compilation flags to freeze Array and Hash literals https://bugs.ruby-lang.org/issues/15393#change-76323 * 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: #@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: #@thing.rb:0 (0,0)-(0,24)> (catch: FALSE) 0000 putobject "a" 0002 putself 0003 opt_send_without_block , 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! -- https://bugs.ruby-lang.org/ Unsubscribe: