$ perl -MO=Deparse -e'print join( "|", %{{ }} = (1)x100 );'
print join('|', %{{};} = (1) x 100);
-e syntax OK
$ perl -e'print join( "|", %{{};} = (1)x100 );'
syntax error at -e line 1, near "%{{};"
Unmatched right curly bracket at -e line 1, at end of line
Execution of -e aborted due to compilation errors.
$