c# - Why does Visual Studio Type a Newly Minted Array as Nullable?

Question

I'm writing a function with a generic type TVal. I wrote this line:

var zeroBased = new TVal[size];

And then in Visual Studio (VS) I used alt+enter to replace var with an explicit type. Here's what I got:

TVal[]? zeroBased = new TVal[size];

I was surprised to find the ? operator, indicating that the type might be nullable. I thought that I'd be safe enough assuming the type is never null when created with new, and could have just done:

TVal[] zeroBased = new TVal[size];

Is there a scenario where instantiating a new array in C# can give you back null?

Note: the code seems to compile fine without the ?, I'm just intrigued by VS's suggestion...

Minimal Verifiable Example

Open Visual Studio, same version as specified below, create a new project, enable nullable types as per the VS Project File Contents below, create a new class, and pop in this function:

public void Test<T>(int size)
{
  var tArr = new T[size];
}

The select the var and hit alt+enter, and choose to replace var with explicit type. If the behaviour is the same as the one I experienced, you'll get:

public void Test<T>(int size)
{
  T[]? tArr = new T[size];
}

Visual Studio Project File Contents

We're using C# 8 for this project and we've enabled Nullables:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <Nullable>enable</Nullable>
    <LangVersion>8.0</LangVersion>
    <WarningsAsErrors>CS8600;CS8602;CS8603</WarningsAsErrors>
    <TargetFramework>netstandard2.0</TargetFramework>
    <OutputType>Library</OutputType>
    <Version>1.0.0.9</Version>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
    <PackageReference Include="System.Dynamic.Runtime" Version="4.3.0" />
  </ItemGroup>

</Project>

Visual Studio Version Info (just bits that seemed important to this Q)

Microsoft Visual Studio Community 2019 Version 16.6.1 VisualStudio.16.Release/16.6.1+30128.74 Microsoft .NET Framework Version 4.7.03062

Installed Version: Community

C# Tools 3.6.0-4.20251.5+910223b64f108fcf039012e0849befb46ace6e66 C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Answer 1

Visual Studio with C# 8 allows you to use nullable types according to the contexts you setup in your project. You can find docs Here.

One way to enable it is with a <Nullable>enable</Nullable> entry in your project file. If you have that then it'll choose to use the nullable type when you convert to explicit variable.

I'm not sure if that same behavior would be used for the other ways - pragmas for example - to enable it. I only tried the project file method.