The second one should be written with curly brackets not parenthesis.

$test = {
test1 => '1',
test2 => '2',
test3 => '3'};
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Otherwise you are trying to assign a list to a scalar. use warnings would have told you this:

Useless use of constants in void context at test.pl line 12.
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This is referring to the members of the list that were discarded when it was assigned to a scalar. Everything but the last 3 was discarded.

Further use strict would have told you:

Can't use string ("3") as a HASH ref while "strict refs" in use at tes
+t.pl line 19.
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$test holds the number 3. When you try to dereference the number 3 (a la %{$test} it converts it to a string "3" and then looks up the hash called "%3" in the symbol table. strict doesn't allow such shenanigans.

The curly brackets in the correct example indicate an anonymous hash reference. References are scalars. So it assigns to $test just fine.

Don't study too hard though - the confusion between references-to-objects and the objects themselves will be going away in Perl 6. (or getting worse, depending how you look at it, :) )

-Andrew.