The type parameters aren't correctly inferred on function pointers

[KyouyamaKazusa0805]

Version Used:

VS 16.9 Preview 2

Steps to Reproduce:

Type code

#nullable enable

using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;

unsafe
{
    string s = new StringBuilder()
        .AppendRange<int, string>(Enumerable.Range(1, 10), &converter) // Here.
        .ToString();
    
    Console.WriteLine(s);
}

static string converter(int v) => $"{v}, ";

public static class C
{
    public static unsafe StringBuilder AppendRange<TElement, TOther>(
        this StringBuilder @this,
        IEnumerable<TElement?> contentList,
        delegate*<TElement?, TOther?> converter)
    {
        foreach (var content in contentList)
        {
            @this.Append(converter(content)?.ToString() ?? string.Empty);
        }

        return @this;
    }
}

The code segment

string s = new StringBuilder()
    .AppendRange<int, string>(Enumerable.Range(1, 10), &converter) // Here.
    .ToString();

should specify type parameters <int, string>.

Expected Behavior:

Because of the type parameters can be inferred from function pointers, so we can omit them:

string s = new StringBuilder()
    .AppendRange(Enumerable.Range(1, 10), &converter)
    .ToString();

Actual Behavior:

An compiler error CS0411 raised: Try to specify type parameters.

[jcouv]

Doesn't repro on latest build (sharplab). I think this was fixed in PR #43041. But that PR pre-dates 16.9p2, so I may be missing something.

@333fred can you confirm and close if appropriate?

[333fred]

I cannot reproduce this on VS 16.9 Preview 2 with the code snippet provided, and this project file:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
  </PropertyGroup>

</Project>

@SunnieShine, is there anything else special about your environment?

[333fred]

@SunnieShine I've been unable to replicate this issue, and am closing it out. If you have more info, please comment and we can reopen.

[333fred]

Hmm, actually, the original snippet has the type parameters there, I misread it. I can reproduce it if I modify the snippet.

[KyouyamaKazusa0805]

@333fred I'm so sorry for late to read your reply. The real problem is that the type parameters can't be omitted.

To be honest, I have the same configuration with yours:

<PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
    <Nullable>enable</Nullable>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
    <LangVersion>9.0</LangVersion>
</PropertyGroup>

Snapshots:

Correct case:

Wrong case:

[333fred]

As I mentioned, I misread your initial snippet. I have a draft out now that should fix the issue.

[KyouyamaKazusa0805]

:)

[333fred]

Fixed in #50249