Rate  using_x assign_undef x_with_value assign_length    assign
using_x       21456/s       --          -5%          -7%          -12%      -13%
assign_undef  22605/s       5%           --          -2%           -8%       -8%
x_with_value  23108/s       8%           2%           --           -5%       -6%
assign_length 24448/s      14%           8%           6%            --       -1%
assign        24637/s      15%           9%           7%            1%        --