Feature #15231


Remove `Object#=~`

Added by mame (Yusuke Endoh) almost 6 years ago. Updated over 5 years ago.

Target version:


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.

["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:

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

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#=~?


  • @usa (Usaku NAKAMURA) 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 #=~.

Updated by naruse (Yui NARUSE) almost 6 years ago

rubocop should alert obj =~ re to fix as re =~ obj.

Actions #2

Updated by znz (Kazuhiro NISHIYAMA) almost 6 years ago

  • Description updated (diff)
Actions #3

Updated by nobu (Nobuyoshi Nakada) almost 6 years ago

  • Description updated (diff)

Updated by sawa (Tsuyoshi Sawada) almost 6 years ago

I agree. At the same time, the String=~ behaviour:

str =~ obj → integer or nil click to toggle source
Match—If obj is a Regexp, use it as a pattern to match against str,and returns the position the match starts, or nil if there is no match. Otherwise, invokes obj.=~, passing str as an argument. The default =~ in Object returns nil.

should be changed to raise a TypeError when obj is not a Regexp, on a par with Regexp#=~ given a non-String argument. Afterall, the following unnatural asymmetry in the current behaviour should be resolved:

// =~ # >> TypeError: no implicit conversion of Object into String
"" =~ # => nil

Updated by znz (Kazuhiro NISHIYAMA) almost 6 years ago

"" =~ "" #=> TypeError (type mismatch: String given)

Updated by matz (Yukihiro Matsumoto) over 5 years ago

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


Actions #7

Updated by mame (Yusuke Endoh) over 5 years ago

  • Status changed from Open to Closed

Applied in changeset trunk|r65984.

lib/webrick: explicitly convert header values to a string

The values of @header are expected to be all strings;
WEBrick::HTTPResponse::[]=(key, val) explicitly converts the second
argument to a string and assigns it to @header hash.
However, there were some points in WEBrick internal code that assigns
non-String to @header. This change fixes the issues.

The values are checked by header_value =~ /\r\n/ in check_header.
The type confusion caused conflict with removal of Object#=~
[Feature #15231].


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