Question

The following code is lifted directly from the source of the Tie::File module. What do the empty parentheses accomplish in the definition of O_ACCMODE in this context? I know what subroutine prototypes are used for, but this usage doesn’t seem to relate to that.

use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY';
sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY }

Answer 1

From perlsub on the topic of constant functions:

Functions with a prototype of () are
potential candidates for inlining