[ruby-core:119664] [Ruby master Bug#20858] multiple parallel assignments are inconsistent

Issue #20858 has been updated by mame (Yusuke Endoh).


Currently, `a, b = c, d = 3, 4` is interpreted as `a, b = c, (d = 3, 4)`. Whether it is good or not.

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Bug #20858: multiple parallel assignments are inconsistent
https://bugs.ruby-lang.org/issues/20858#change-110320

* Author: daveola (David Stellar)
* Status: Open
* ruby -v: ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
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I may have terminology wrong, so apologies.  For this bug I'm going to use "multiple assignment" to refer to using multiple assignment operators in a line, such as:

``` ruby
a = b = c = 1
```

And then parallel assignment to refer to doing multiple assignments at the same time using tuples, such as:

``` ruby
a,b = 1, 2
```

Unfortunately combining these is inconsistent.  First of all, just doing this:

``` ruby
a,b = c,d = 3,4
```

Gives us:  **"undefined local variable or method `c' for main (NameError)"**

So if we work around that by defining all our variables, we then get unexpected results:

``` ruby
a = b = c = d = 'foobar'

a,b = c,d = 3,4

puts "Got:  a=#{a} b=#{b} and c=#{c} d=#{d}"
# Got:  a=foobar b=3 and c=foobar d=3

c,d = 3,4
a,b = c,d

puts "Got:  a=#{a} b=#{b} and c=#{c} d=#{d}"
# Got:  a=3 b=4 and c=3 d=4
```


I can imagine that if multiple parallel assignment is not supported that a,b will not get set properly, but it does not follow that c would be undefined by the expression.



-- 
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