From: eregontp@... Date: 2018-12-15T13:27:04+00:00 Subject: [ruby-core:90549] [Ruby trunk Feature#15393] Add compilation flags to freeze Array and Hash literals Issue #15393 has been updated by Eregon (Benoit Daloze). 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) ``` 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. ---------------------------------------- Feature #15393: Add compilation flags to freeze Array and Hash literals https://bugs.ruby-lang.org/issues/15393#change-75698 * 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! ---Files-------------------------------- 0001-Add-compile-options-for-freezing-hash-and-array-lite.patch (6.14 KB) -- https://bugs.ruby-lang.org/ Unsubscribe: