Issue #9593 has been updated by Nobuyoshi Nakada.


Yes, it's a very old bug.
Optional arguments have same semantics as assignments.

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Bug #9593: Keyword arguments default argument assignment behaviour not consistent with optional argument
https://bugs.ruby-lang.org/issues/9593#change-45765

* Author: Jack Chen
* Status: Closed
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Category: syntax
* Target version: current: 2.2.0
* ruby -v: 2.1.1
* Backport: 1.9.3: REQUIRED, 2.0.0: REQUIRED, 2.1: REQUIRED
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Given the following code:

    def var
      100
    end

    def foo(var: var + 1)
      puts "var: #{var.inspect}"
    end

    def bar(var = var + 1)
      puts "var: #{var.inspect}"
    end

    foo(var: 1)
    foo rescue p $!

    bar(1)
    bar

Ruby 2.0.0:

    var: 1
    var: 101
    var: 1
    var: 101

Ruby 2.1.1:

    var: 1
    #<NoMethodError: undefined method `+' for nil:NilClass>
    var: 1
    var: 101

What appears to be happening is that since 2.1.1, the keyword argument defines `var` as a variable before evaluating the default argument. Personally, I prefer 2.0.0 behaviour, but the way 2.1.1 handles default arguments in non keyword arguments is inconsistent.



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