Can't use C# .NET 6 PriorityQueue in Unity

Question

I'm trying to use PriorityQueue in Unity with C#. The documentation says that it's supported in .NET 6 in namespace System.Collections.Generic.

I've tried:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using TMPro;

public class Test : Monobehaviour
{
    void Start()
    {
        var queue = new PriorityQueue<int, int>();
    }
}

But an error is thrown back:

The type or namespace name 'PriorityQueue<,>' could not be found (are
you missing a using directive or an assembly reference?)
[Assembly-CSharp]

I've checked the .NET version within VS Code:

Why doesn't it work in Unity?

Institutional

What is the target framework version in the project file? Just running dotnet from a prompt doesn't prove much. – Hyposensitize

@JeroenMostert I found this in the .csproj file <TargetFrameworkVersion>v4.7.1</TargetFrameworkVersion>. This is the problem? – Institutional

Well yes, it's obviously targeting .NET 4.7.1, and given the name of that element this is an old-style .csproj, not the new-style (that uses TargetFramework and TargetFrameworks, and is a lot shorter besides). I'm not sure Unity even has support for .NET Core (yet), which 6 is, but that's another question. – Hyposensitize

@JeroenMostert I'm currently using Unity 2020.3, a bit behind now, not sure if that's the problem. – Institutional

@JeroenMostert just search around in Unity doc 2020.3 a bit, said that .NET standard 2.0 and .NET 4.x are supported. Yeah... Seems like even Unity 2022.1 doc said the same thing, so... – Institutional

Fortunately priority queues are not rocket science (if that's the only thing you're going for in terms of .NET 6); compatible implementations should be easy to find. Sufficiently unimportant queues that aren't crucially dependent on performance can even be faked with other data structures (like a SortedList or SortedDictionary using a tuple that includes the priority and an ID for uniqueness, with only the priority used for sorting through a custom comparer). – Hyposensitize

I have the same issue. I checked visual studio installer and know .NET 6 is installed. Project target framework is .NET Framework 4.8. I'm also just using this in a console application in visual studio, nothing special like unity involved. – Palpate

Answer 1

The version reported by dotnet is completely unrelated to Unity's C#/.NET version (at least until Unity finally migrates from Mono). While the language supported is almost equal to C# 9.0, the actual library that is used is a loose superset of what Mono provides, and actually is roughly equal to .NET Framework 4.8/.NET Standard 2.0 ATM; since neither of those has PriorityQueue, it's not available. You can either:

• wait for the transition to .NET 6/7 happen (be aware it may take a couple of years :),
• use a 3rd party implementation,
• implement it yourself,
• copy-paste the code from the official source (minor tweaks will be required for it to work) or
• use this direct port from official C# lib (single-file drop-in, ported by me, open source, no string attached).

Veron

Yeah, I have imported C5 and used their IntervalHeap since then, pretty fine! – Institutional