Laravel Attach Role using Select Box

i'm trying to attach role for user using select box but it doesn't work

i've Roles table and bridge table between Roles and Users Table

i know it's many-to-many relationship and i should use check boxes instead of select box

but at the time for some reason i need to assign only 1 Role for user

So, i have to use select box

Any ideas?

Controller

public function store(Request $request)
{
    $this->validate($request, array(
        'name'         => 'required|string|max:255',
        'email'          => 'required|string|email|max:255|unique:users',
        'password'          => 'required|string|min:8',
    ));
    $password = Hash::make($request->password);
    $user = new User;
    $user->name = $request->input('name');
    $user->email = $request->input('email');
    $user->password = $password;
    $user->save();

    if ($request['user']) {
        $user->roles()->attach(Role::where('name','user')->first());
    }
    if ($request['editor']) {
        $user->roles()->attach(Role::where('name','editor')->first());
    }
    if ($request['admin']) {
        $user->roles()->attach(Role::where('name','admin')->first());
    }

    return redirect('users')->with('success', 'user is successfully saved');
}

View

                        <div class="form-group">
                            <label class="col-12">Roles</label>
                            <div class="col-12">
                                <div class="custom-control custom-radio mb-5">
                                    <input class="custom-control-input" type="radio" name=admin" id="example-radio1" value="admin">
                                    <label class="custom-control-label" for="example-radio1">Admin</label>
                                </div>
                                <div class="custom-control custom-radio mb-5">
                                    <input class="custom-control-input" type="radio" name=pharmacy" id="example-radio2" value="editor">
                                    <label class="custom-control-label" for="example-radio2">Editor</label>
                                </div>
                                <div class="custom-control custom-radio mb-5">
                                    <input class="custom-control-input" type="radio" name=company" id="example-radio3" value="user">
                                    <label class="custom-control-label" for="example-radio3">User</label>
                                </div>
                            </div>
                        </div>

via Chebli Mohamed