# How to use a type wrapping a Symbol as a type parameter?

**URL:** <https://discourse.julialang.org/t/how-to-use-a-type-wrapping-a-symbol-as-a-type-parameter/19628>\
**Category:** General Usage\
**Created:** [January 14, 2019, 5:03pm UTC](https://discourse.julialang.org/t/how-to-use-a-type-wrapping-a-symbol-as-a-type-parameter/19628 "2019-01-14T17:03:24Z")\
**Posts on this page:** 1\
**Showing post:** 6

<div class="post-metadata">

**Author:** ![jekbradbury](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jekbradbury/32/953_2.png) [@jekbradbury](https://discourse.julialang.org/u/jekbradbury)\
**Post date:** [January 15, 2019, 5:06am UTC](https://discourse.julialang.org/t/how-to-use-a-type-wrapping-a-symbol-as-a-type-parameter/19628/6 "2019-01-15T05:06:54Z")

</div>

The relevant check appears to be [this runtime function](https://github.com/JuliaLang/julia/blob/7772486a6942c9a9b52849b6ffe690a7da5861cd/src/builtins.c#L825-L843):

```julia
static int valid_type_param(jl_value_t *v)
{
    if (jl_is_tuple(v)) {
        // NOTE: tuples of symbols are not currently bits types, but have been
        // allowed as type parameters. this is a bit ugly.
        jl_value_t *tt = jl_typeof(v);
        size_t i, l = jl_nparams(tt);
        for(i=0; i < l; i++) {
            jl_value_t *pi = jl_tparam(tt,i);
            if (!(pi == (jl_value_t*)jl_sym_type || jl_isbits(pi)))
                return 0;
        }
        return 1;
    }
    if (jl_is_vararg_type(v))
        return 0;
    // TODO: maybe more things
    return jl_is_type(v) || jl_is_typevar(v) || jl_is_symbol(v) || jl_isbits(jl_typeof(v));
}

```

I wonder if you could just add stuff there…

---

_[View the full topic](https://discourse.julialang.org/t/how-to-use-a-type-wrapping-a-symbol-as-a-type-parameter/19628)._