[ruby-core:99009] [Ruby master Feature#17004] Provide a way for methods to omit their return value

Issue #17004 has been updated by Eregon (Benoit Daloze).


What Jeremy said, so in short RubyVM is not a good place for this because it's CRuby-specific (ExperimentalFeatures or Kernel would be OK IMHO).

Do you have measurements on real applications, not just micro-benchmarks?

The masgn case (`'1.times {|i| x, y = self, i }'`) could be done transparently by the VM without exposing any predicate.
Same for core methods like String#slice!.
I'm not sure if it's a good idea to expose this to Ruby (and C ext) users, it seems very low level.
At least, I think we should take advantage of this in language/core before exposing to users.

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Feature #17004: Provide a way for methods to omit their return value
https://bugs.ruby-lang.org/issues/17004#change-86384

* Author: shyouhei (Shyouhei Urabe)
* Status: Open
* Priority: Normal
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In ruby, it often is the case for a method's return value to not be used by its caller.  Even when a method returns something meaningful, its caller is free to ignore it.

Why not provide a way for a method to know if its return value is needed or not?  That adds a room for methods to be optimized, by for instance skipping creation of complex return values.

The following pull request implements `RubyVM.return_value_is_used?` method, which does that: https://github.com/ruby/ruby/pull/3271



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