The () prototype is there to enable inlining the constants, making the code a bit more efficient.

From perlsub:

Functions with a prototype of "()" are potential candidates for inlining. If the result after optimization and constant folding is either a constant or a lexically- scoped scalar which has no other references, then it will be used in place of function calls made without "&". Calls made using "&" are never inlined. (See constant.pm for an easy way to declare most constants.)
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: What are the brackets in this for ? by Joost
in thread What are the brackets in this for ? by nbowden

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