BuddyPress | Check if user is in current group [closed]

I’m developing a plugin for a website, which uses the Group Extension API to create a new “subpage” in the group’s page, just like Home, Members…

Here’s the code:

class BP_Suggest extends BP_Group_Extension {

...

function display() {
    global $bp; 
    $group_id = $bp->groups->current_group->id;
    ?>
        <h2>
            Suggest Ideas to the group.
        </h2>
        <?php $this->print_all_suggestions($group_id); ?>


    <?php
}

...

I want to print, before the $this->print_all_suggestions($group_id); function, a form for posting a suggestion – but to print this form only is the user is logged in and is a member of the current group (which I have the ID of, like you’ve seen in line 2 of the function display())
:

if(is_user_a_member_of_this_group()):
?>
    <div>
    ....
    </div>
<?php
else:
    echo "You don't have permissions to post here";
endif;

What should the function is_user_a_member_of_this_group() contain? (I’ll probably change the name, don’t worry 😉 )

Thanks!

function is_user_a_member_of_this_group($user_id, $group_id)
    //return: bool
    return groups_is_user_member( $user_id, $group_id );
}