ruby-core

Issue #7314 has been updated by Shyouhei Urabe.


We looked at this issue in yesterday's developer meeting.

The use case Andrew showed is (in spite of his intention) not unpredictable.  Rather, if we allowed proc->lambda transformation, it gets unpredictable for a proc body what to expect for its first argument.

When writing a proc literal, its programmer's intention is clear that they wanted proc-style behaviour in mind.  Currently if a block starts with "lambda {", it behaves like a lambda.  All others are proc.  This is consistent.  But if we introduce proc conversion, this intension breaks. You can't predict what would happen when a proc is actually called during you write that proc; because it can be converted later.  This is bad.



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Feature #7314: Convert Proc to Lambda doesn't work in MRI
https://bugs.ruby-lang.org/issues/7314#change-58721

* Author: Richard Schneeman
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
I have code where I need to convert a proc to a lambda (i need to be able to return out of the block). I would expect that passing a proc into a lambda to return a lambda. When I run this code on MRI i do not get the result I would expect

```ruby
my_proc = proc { |x| x }
my_lambda = lambda &my_proc
my_lambda.lambda?
```

The result is `false` but I would expect it to be  `true`

There is currently a way to turn a proc into a lambda in MRI like this: 

```ruby
def convert_to_lambda &block
  obj = Object.new
  obj.define_singleton_method(:_, &block)
  return obj.method(:_).to_proc
end
```

But this feels like a hack, and is not supported across other implementations. I would expect that passing a proc into a lambda to return a lambda, I believe it is a bug.






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