The behavior of this script in perl 5.26 is so weird that it seems like it must be a bug. 
Before calling the sub test_this @arr: 1 2 3 4 5 6 7 8 9 10
Inside the sub, before the map @arr: 1 2 3 4 5 6 7 8 9 10
Inside the sub, before the map @_ = 1 2 3 4 5 6 7 8 9 10
Inside the sub, after the map @arr: 2 4 6 8 10 12 14 16 18 20
Use of uninitialized value $_[0] in join or string at foo line 11.
Use of uninitialized value $_[3] in join or string at foo line 11.
Use of uninitialized value $_[6] in join or string at foo line 11.
Use of uninitialized value $_[9] in join or string at foo line 11.
Inside the sub, after the map @_ =  _ Use of uninitialized value $_[0]
+ in join or string at foo line 11.
  _ Use of uninitialized value $_[3] in join or string at foo line 11.
  _ Use of uninitialized value $_[6] in join or string at foo line 11.
 
After calling the sub test_this @arr: 2 4 6 8 10 12 14 16 18 20

[download]
If I throw in print Dumper(@_), I get this: 
panic: attempt to copy freed scalar 7fe03e8040b0 to 7fe03e82c858 at /o
+pt/local/lib/perl5/5.26/darwin-thread-multi-2level/Data/Dumper.pm lin
+e 602.

[download]
Anyone know what's going on?

In reply to Re: How come @_ gets changed here? by Anonymous Monk
in thread How come @_ gets changed here? by pritesh_ugrankar

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