Attribute::Constant/Data::Lock claims to be faster than *glob = \'constant', both of which are lots faster than Readonly

$ perl -le " use Attribute::Constant; my $pi : Constant( 3.14159265358
+9793 ); print $pi; $pi++"
3.14159265358979
Modification of a read-only value attempted at -e line 1.
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