[ruby-core:96373] [Ruby master Bug#16406] `(lambda_proc << normal_proc).lambda?` should return false

Issue #16406 has been updated by ko1 (Koichi Sasada).


It was discussed and Matz approved to fix it after Ruby 2.7 release.


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Bug #16406: `(lambda_proc << normal_proc).lambda?` should return false
https://bugs.ruby-lang.org/issues/16406#change-83288

* Author: alanwu (Alan Wu)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
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Consider:

```ruby
plus = proc { |a, b| a + b }
mult_two = ->(x) { x * 2 }
composed = mult_two << plus
p [composed. lambda?, composed.call([1, 2])]
```
I think this ought to print `[false, 6]` instead of `[true, 6]`, as the call `composed.call([1, 2])` is clearly not using lambda semantics.
Since `composed = f << g` calls `g` first, I think it makes sense to report `#lambda?` based on whether `g` has lambda semantics.
I have a pull request at https://github.com/ruby/ruby/pull/2729 to make this change.




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