Add string to array based on flag
strings are probably the wrong choice to represent roles. You lose the power of the type system -- the compiler won't pick up on typos, e.g. "Amdin". Consider using an enum instead.

Be consistent with your naming. Why is it USER_ROLES.IsRead and USER_ROLES.Write (not IsWrite)? Stick to the standard naming conventions, e.g. write UserRole.IsRead instead of USER_ROLES.IsRead.

Does the calling code really need an array returned? It would probably be fine with an IEnumerable.

If we change the return type to IEnumerable&lt;UserRole&gt;, we can write

public IEnumerable&lt;UserRole&gt; GetRoles()
{
    if (this.IsAdmin)
    {
        yield return UserRole.Admin;
    }

    if (this.IsRead)
    {
        yield return UserRole.Read;
    }

    if (this.IsWrite)
    {
        yield return UserRole.Write;
    }

    if (this.IsEntityUser)
    {
        yield return UserRole.EntityUser;
    }
}


But I'm guessing you're asking more about the repetition. Here's one way to get around it -- create an association between the booleans and the values. Here I've used a dictionary; it's possibly a bit of overkill but it does give us the nice initialiser syntax:

public IEnumerable&lt;UserRole&gt; GetRoles()
{
    var roles = new Dictionary&lt;UserRole, bool&gt;
    {
        { UserRole.Admin, this.IsAdmin },
        { UserRole.Read, this.IsRead },
        { UserRole.Write, this.IsWrite },
        { UserRole.EntityUser, this.IsEntityUser }
    };
    return roles.Where(role =&gt; role.Value)
                .Select(role =&gt; role.Key);
}


Other options would be an array of KeyValuePairs, an array of Tuples, etc.