# Removing ambiguity warnings from Julia v0.4

**URL:** <https://discourse.julialang.org/t/removing-ambiguity-warnings-from-julia-v0-4/1748>\
**Category:** General Usage\
**Created:** [January 29, 2017, 4:58am UTC](https://discourse.julialang.org/t/removing-ambiguity-warnings-from-julia-v0-4/1748 "2017-01-29T04:58:46Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![kevin.squire](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kevin.squire/32/62_2.png) [@kevin.squire](https://discourse.julialang.org/u/kevin.squire)\
**Post date:** [January 29, 2017, 4:58am UTC](https://discourse.julialang.org/t/removing-ambiguity-warnings-from-julia-v0-4/1748/1 "2017-01-29T04:58:46Z")

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I’m updating the `SortedSet` constructors in `DataStructures.jl`, and I’m having trouble removing a particular ambiguity warning from Julia v0.4. The code works fine in v0.5 and v0.6 (and not just because [ambiguity warnings were moved to runtime](https://github.com/JuliaLang/julia/issues/16125)).

The warning stems from

```julia
SortedSet{O<:Ordering}(o::O, iter) = sortedset_with_eltype(o, iter, eltype(iter))
SortedSet{O<:Ordering}(iter, o::O) = sortedset_with_eltype(o, iter, eltype(iter))

```

This makes sense–if one calls this constructor with two `Ordering`s, the call is ambiguous (even if this unlikely to happen).

The actual warning, however, is

```cpp
WARNING: New definition
    call(Type{DataStructures.SortedSet}, Any, #O<:Base.Order.Ordering) at /Users/kevin/.julia/v0.4/DataStructures/src/sorted_set.jl:30
is ambiguous with:
    call(Type{DataStructures.SortedSet}, #O<:Base.Order.Ordering, Any) at /Users/kevin/.julia/v0.4/DataStructures/src/sorted_set.jl:29.
To fix, define
    call(Type{DataStructures.SortedSet}, _<:Any, _<:Any)
before the new definition.

```

The warning itself is slightly unclear (I’m pretty sure `_` is a type variable), but I believe either of the following definitions should handle the actual ambiguity:

```julia
SortedSet(::Ordering,::Ordering) = throw(ArgumentError("SortedSet with two parameters must be called with an Ordering and an interable"))
SortedSet{T}(::T,::T) = throw(ArgumentError("SortedSet with two parameters must be called with an Ordering and an interable"))

```

Unfortunately, neither does. Am I missing something, or is this an issue with the parser in v0.4?

With v0.6 around the corner, this arguably isn’t that important. But there’s a desire to continue to support DataStructures.jl on v0.4, so it would be nice not to introduce this warning.

Any thoughts welcome!

Cheers,  
Kevin

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<div class="post-metadata">

**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [January 29, 2017, 5:39am UTC](https://discourse.julialang.org/t/removing-ambiguity-warnings-from-julia-v0-4/1748/2 "2017-01-29T05:39:54Z")

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> [@kevin.squire](#):
>
> SortedSet{T}(::T,::T) = throw(ArgumentError(“SortedSet with two parameters must be called with an Ordering and an interable”))

This won’t. It’ll just introduce more ambiguity. The other one is probably a bug in the type system.

---

<div class="post-metadata">

**Author:** ![kevin.squire](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kevin.squire/32/62_2.png) [@kevin.squire](https://discourse.julialang.org/u/kevin.squire)\
**Post date:** [January 29, 2017, 6:10am UTC](https://discourse.julialang.org/t/removing-ambiguity-warnings-from-julia-v0-4/1748/3 "2017-01-29T06:10:06Z")

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Thanks, @yuyichao.

I was able to get around it by removing the `O<:Ordering` parameterization and just using `Ordering` directly in the signature:

```julia
SortedSet(o::Ordering, iter) = sortedset_with_eltype(o, iter, eltype(iter))
SortedSet(iter, o::Ordering) = sortedset_with_eltype(o, iter, eltype(iter))

```

In the original definition, `O` wasn’t used, so it absolutely didn’t need to be there. A second set of similar definitions did use the parameterization, but it wasn’t to hard to change the definition not to use it.

Cheers,  
Kevin