[ruby-core:122847] [Ruby Feature#21520] Feature Proposal: Enumerator::Lazy#peek
Issue #21520 has been reported by nuzair46 (Nuzair Rasheed). ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I would be glad to work on this and make a PR. Thank you. -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I would be glad to work on this and make a PR. Thank you. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520#change-114137 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I would be glad to work on this and make a PR. Thank you. -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by Dan0042 (Daniel DeLorme). #peek already exists, and does something different. I think #each should work in the way this proposal describes. I was a bit surprised that the code below resulted in an infinite loop rather than a lazy enumeration. ```ruby (1..).lazy.each{ |x| puts x }.select(&:even?).first(3) ``` ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520#change-114146 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I would be glad to work on this and make a PR. Thank you. -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). Dan0042 (Daniel DeLorme) wrote in #note-2:
#peek already exists, and does something different.
Hey, Enumerator#peek exists. but Enumerator::Lazy#peek does not. Enumerator#peek [works differently](https://docs.ruby-lang.org/ja/latest/method/Enumerator/i/peek.html) than this suggestion. So maybe the naming will be confusing. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520#change-114155 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I would be glad to work on this and make a PR. Thank you. -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). nuzair46 (Nuzair Rasheed) wrote in #note-3:
Enumerator#peek [works differently](https://docs.ruby-lang.org/ja/latest/method/Enumerator/i/peek.html) than this suggestion. So maybe the naming will be confusing.
Running the whole CI, I see the collision with Enumerator#peek. So I think the name should be changed to avoid confusion and collision. Im thinking `spy` or `tap_each` ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520#change-114171 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nobu (Nobuyoshi Nakada). Or `lazy_each`? ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#peek https://bugs.ruby-lang.org/issues/21520#change-114183 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #peek method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#peek, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .peek { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .peek { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #peek is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #peek is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). Subject changed from Feature Proposal: Enumerator::Lazy#peek to Feature Proposal: Enumerator::Lazy#lazy_each Description updated updated to `lazy_each` ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#lazy_each https://bugs.ruby-lang.org/issues/21520#change-114186 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #lazy_each method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#lazy_each, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .lazy_each { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .lazy_each { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #lazy_each is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #lazy_each is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). The PR is open for review https://github.com/ruby/ruby/pull/14024 ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#lazy_each https://bugs.ruby-lang.org/issues/21520#change-114217 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #lazy_each method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#lazy_each, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .lazy_each { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .lazy_each { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #lazy_each is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #lazy_each is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nobu (Nobuyoshi Nakada). A couple days ago, another name came to me: `tee`. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#lazy_each https://bugs.ruby-lang.org/issues/21520#change-114304 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #lazy_each method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#lazy_each, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .lazy_each { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .lazy_each { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #lazy_each is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #lazy_each is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). nobu (Nobuyoshi Nakada) wrote in #note-9:
A couple days ago, another name came to me: `tee`.
Thanks, `tee` is a great fit. It’s short and feels very Unix-y. I will make changes to the PR and the proposal soon. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#lazy_each https://bugs.ruby-lang.org/issues/21520#change-114306 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #lazy_each method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#lazy_each, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .lazy_each { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .lazy_each { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #lazy_each is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #lazy_each is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by matz (Yukihiro Matsumoto). I don't think `lazy_each` is a good name. We just wanted to peek the element in the stream, being lazy or not. In that sense, `tee` is better, if you are familiar with UNIX (like me). Matz. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#lazy_each https://bugs.ruby-lang.org/issues/21520#change-114310 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #lazy_each method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#lazy_each, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .lazy_each { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .lazy_each { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #lazy_each is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #lazy_each is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
Issue #21520 has been updated by nuzair46 (Nuzair Rasheed). matz (Yukihiro Matsumoto) wrote in #note-11:
I don't think `lazy_each` is a good name. We just wanted to peek the element in the stream, being lazy or not. In that sense, `tee` is better, if you are familiar with UNIX (like me).
Matz.
Thanks Matz. I have updated the PR and proposal with the name #tee for the method. ---------------------------------------- Feature #21520: Feature Proposal: Enumerator::Lazy#tee https://bugs.ruby-lang.org/issues/21520#change-114316 * Author: nuzair46 (Nuzair Rasheed) * Status: Open ---------------------------------------- # Abstract Add a #tee method to Enumerator::Lazy that allows observing each element in a lazy enumeration pipeline without modifying or consuming the stream. # Background Ruby provides Enumerator::Lazy for efficient lazy stream processing. However, unlike languages such as Java, it lacks a clean way to inspect intermediate elements during lazy evaluation. Currently, developers must misuse .map for side effects, example: ```rb (1..).lazy.map { |x| puts x; x }.select(&:even?).first(3) ``` This is semantically incorrect and confusing, since .map implies transformation, not observation. # Proposal Introduce Enumerator::Lazy#tee, which yields each item to a block and returns the item unmodified, similar to Object#tap, but in a lazy stream: ```rb (1..).lazy .tee { |x| puts "saw: #{x}" } .select(&:even?) .first(3) ``` This would be equivalent to: ```rb lazy.map { |x| block.call(x); x } ``` but with improved semantic clarity. # Use cases • Debugging lazy enumerators without breaking the chain • Logging or instrumentation in pipelines • Educational / demo use for showing lazy evaluation step-by-step • Cleaner replacement for map { puts x; x } hacks Example: ```rb data = (1..).lazy .tee { |x| puts "got #{x}" } .select(&:even?) .first(5) ``` result: ```rb got 1 got 2 got 3 got 4 got 5 ... got 10 ``` And return [2, 4, 6, 8, 10] # Discussion #tee is a minimal, non-breaking addition that improves clarity and idiomatic usage of Enumerator::Lazy. It avoids abusing .map for observation and is familiar to developers from other languages. #tee is also not needed for other enumerators where .tap or .each can do the job. It mirrors Java’s .stream().peek(...) and makes Ruby’s lazy enumeration more expressive and readable. # See also • [Java Stream.peek](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#peek-...) I have a draft PR for the implementation ready https://github.com/ruby/ruby/pull/14024 -- https://bugs.ruby-lang.org/
participants (4)
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Dan0042 (Daniel DeLorme) -
matz (Yukihiro Matsumoto)
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nobu (Nobuyoshi Nakada)
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nuzair46 (Nuzair Rasheed)