Eliminate implicit magic in Proc.new and Kernel#proc
Proc.new and Kernel#proc have a little known feature: if called without a block, they capture whatever block was passed to the current method.
I propose that this feature should be removed, finally, since it:
- Doesn't enhance readability (where is this block coming from?)
- Doesn't reflect any other behavior in Ruby
- Can lead to bugs (call either without a block accidentally and you aren't sure what you'll get)
I believe this was an implementation artifact in MRI, since the most recently-pushed block would still be on global stacks, which is where the logic for proc and Proc.new looked for it.
All argument syntaxes now support &block, which I believe is the correct way to clearly, explicitly capture the incoming block into an object.