[ruby-core:89986] [Ruby trunk Feature#15231] Remove `Object#=~`

[matz@ruby-lang.org]

Issue #15231 has been updated by matz (Yukihiro Matsumoto).


I vote for the proposed change. Let's give deprecation warning first. I don't think we need to remove `!~` from `Kernel`.

Matz.


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Feature #15231: Remove `Object#=~`
https://bugs.ruby-lang.org/issues/15231#change-75091

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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`Object#=~` receives (and just discards) an argument, and always returns nil.  What purpose is this method for?

The following behavior that `Object#=~` caused was confusing to me.

```RUBY
["foo"] =~ /foo/ #=> nil
```

More precisely: the actual example that I encountered was to parse coverage data from output of coverage measurement tool by using `Open3.capture2`:

```RUBY
out = Open3.capture2("gcov", ...) # BUG: `out, =` was intended
if out =~ /lines\.*: *(\d+\.\d+)%/
  ...
end
```

Obviously, I forgot a comma to receive the return value of `Open3.capture2`.  The method returns a two-element array, and `out =~` calls `Object#=~`, which hid the bug.  (Worse, I took several tens of minutes to debug it because I first thought that this is a bug of regexp, and spent tweaking the regexp.)

I guess `Object#=~` was intended for general pattern matching, but presently the role was taken over by `Object#===`.


So.  How about removing `Object#=~`?

Concerns:

* @usa said `NilClass#=~` should be newly introduced because of: `if gets =~ /re/`
* `Object#!~` is difficult to remove: some classes define only `#=~`, and expect `Object#!~` to delegate to `#=~`.



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