```{index} single: is_sub_constant (Sub::Identify) ``` ```{index} single: Sub::Identify::is_sub_constant ``` # is_sub_constant Whether a sub is a constant perl inlines. ## Synopsis ```perl use Sub::Identify qw(is_sub_constant); use constant PI => 3.14159; is_sub_constant(\&PI); # true is_sub_constant(sub () { $x }); # false: it closes over $x ``` ## What you get back True for a sub with an empty prototype that perl has made a constant - `use constant`, or `sub () { LITERAL }` - and false for everything else, including a non-reference.