Array#initialize_copy

VALUE
rb_ary_replace(VALUE copy, VALUE orig)
{
    rb_ary_modify_check(copy);
    orig = to_ary(orig);
    if (copy == orig) return copy;

    if (RARRAY_LEN(orig) <= RARRAY_EMBED_LEN_MAX) {
        VALUE shared_root = 0;

        if (ARY_OWNS_HEAP_P(copy)) {
            ary_heap_free(copy);
        }
        else if (ARY_SHARED_P(copy)) {
            shared_root = ARY_SHARED_ROOT(copy);
            FL_UNSET_SHARED(copy);
        }
        FL_SET_EMBED(copy);
        ary_memcpy(copy, 0, RARRAY_LEN(orig), RARRAY_CONST_PTR_TRANSIENT(orig));
        if (shared_root) {
            rb_ary_decrement_share(shared_root);
        }
        ARY_SET_LEN(copy, RARRAY_LEN(orig));
    }
    else {
        VALUE shared_root = ary_make_shared(orig);
        if (ARY_OWNS_HEAP_P(copy)) {
            ary_heap_free(copy);
        }
        else {
            rb_ary_unshare_safe(copy);
        }
        FL_UNSET_EMBED(copy);
        ARY_SET_PTR(copy, ARY_HEAP_PTR(orig));
        ARY_SET_LEN(copy, ARY_HEAP_LEN(orig));
        rb_ary_set_shared(copy, shared_root);
    }
    ary_verify(copy);
    return copy;
}