Its not clear to me what the "avoiding dereferencing side effects" part of the documentation means exactly, however I feel pretty confident in saying that it isnt relevent here. When you do 

$hash{key}.=$str;

[download]

there is no dereferencing going on. With 

$hash->{key}.=$str;

[download]

there is, however it happens before the .= operator is involved, so it doesnt explain the special casing behaviour of .= and other mutator operators. It turns out that the documentation of this behaviour is not to be found in perlop, but rather in perlsyn (in the section Declarations): 

Operators such as ++, --, +=, -=, and .=, that operate on undefined le
+ft values such as:

    my $a;
    $a++;

are also always exempt from such warnings.

[download]

Hope this clears things up for you.

---
$world=~s/war/peace/g

In reply to Re^5: problem unless I use ".=" by demerphq
in thread problem unless I use ".=" by cgmd

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