From 26475d0a7897c25f8632b776014a19c3a6f6ecc2 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Sun, 25 Nov 2018 18:03:27 +0900
Subject: Update `doc/limitations.md` for argument destructuring.

---
 doc/limitations.md | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

(limited to 'doc')

diff --git a/doc/limitations.md b/doc/limitations.md
index 92858cb1f..825435f01 100644
--- a/doc/limitations.md
+++ b/doc/limitations.md
@@ -219,7 +219,7 @@ $ ruby -e 'def m(*r,**k) p [r,k] end; m("a"=>1,:b=>2)'
 [[{"a"=>1}], {:b=>2}]
 ```
 
-#### mruby []
+#### mruby [mruby 2.0.0]
 
 ```
 $ ./bin/mruby -e 'def m(*r,**k) p [r,k] end; m("a"=>1,:b=>2)'
@@ -227,3 +227,23 @@ trace (most recent call last):
 	[0] -e:1
 -e:1: keyword argument hash with non symbol keys (ArgumentError)
 ```
+
+## Argument Destructuring
+
+```ruby
+def m(a,(b,c),d); p [a,b,c,d]; end
+m(1,[2,3],4)  # => [1,2,3,4]
+```
+Destructured arguments (`b` and `c` in above example) cannot be accessed
+from the default expression of optional arguments and keyword arguments,
+since actual assignment is done after the evaluation of those default
+expressions. Thus:
+    
+```ruby
+def f(a,(b,c),d=b)
+  p [a,b,c,d]
+end
+f(1,[2,3])
+```
+
+CRuby gives `[1,2,3,nil]`. mruby raises `NoMethodError` for `b`.
-- 
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