You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: register.m
    path of file: ./repos/unified_tracking_benchmark/utils
    
    the code of the file until where you have to start completion: function [set] = register(set_name, object)

    
function [set] = register(set_name, object)
%REGISTER Register an object to a internal set
%
% REGISTER(SET_NAME, OBJECT)
%   will register the OBJECT to the internal set identified as SET_NAME.
%
% REGISTER(SET_NAME, 'clear')
%   will clear all the registered obejcts.
%
% SET = REGISTER(SET_NAME, ...)
%   will return the SET containing all the registered obejcts.
%
% Input:
% - SET_NAME (string): Name of the specified set.
% - OBJECT (struct): The obejct to register.
%
% Output:
% - SET (cell, struct): An 1D cell array of structs.
%

persistent registered_sets;

if ~exist('registered_sets', 'var')
    registered_sets = struct();
end