facility for creating read-only scalars, arrays, and hashes

 Const::Fast is a perl module for creating read-only scalars, arrays,
 and hashes. It enables you to set a variable to the given value and
 subsequently make it readonly. Arrays and hashes will be made deeply
 readonly.
 .
 This module uses the builtin readonly feature of perl, making access
 to the variables just as fast as any normal variable without the
 weird side-effects of ties.