use strict;
use warnings;
use Benchmark 'cmpthese';

cmpthese -1, { map { $_ => \&$_ } 'a' .. 'g' };

                                         sub a {eval 1 for 0 .. 999}
{use feature ':5.10';                    sub b {eval 1 for 0 .. 999}}
{use 5.010;                              sub c {eval 1 for 0 .. 999}}
{no feature ':all'; use feature ':5.10'; sub d {eval 1 for 0 .. 999}}

{use feature 'say';                   sub e {eval 1 for 0 .. 999}}
{                   no feature 'say'; sub f {eval 1 for 0 .. 999}}
{use feature 'say'; no feature 'say'; sub g {eval 1 for 0 .. 999}}
[download]

Results:

   Rate    d    b    e    g    f    a    c
d 119/s   --  -0% -18% -23% -25% -53% -53%
b 119/s   0%   -- -18% -23% -25% -53% -53%
e 145/s  22%  22%   --  -7%  -8% -43% -43%
g 155/s  30%  30%   7%   --  -2% -38% -38%
f 158/s  33%  33%   9%   2%   -- -37% -37%
a 252/s 112% 112%  74%  62%  59%   --  -0%
c 252/s 112% 112%  74%  63%  59%   0%   --
[download]

Looks like feature pragma leaves some nasty attribute somewhere if mentioned. String eval is slow as it is already, why make it even slower. Well, partly tongue-in-cheek useless entertainment, but still partly: I used to declare like "c" case, then made a habit of explicitly declaring like e.g. "e"; now what? perfectionist in me urges to return to habits of years long gone. The "d" is there because feature says it should be exactly the same as "c".

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