IsExternalInit

Compiler polyfill that enables C# 9 init-only property accessors in Unity projects targeting .NET Standard 2.1. This is a zero-cost, marker-only class with no runtime behavior.

Definition

Namespace: System.Runtime.CompilerServices Assembly: Paragon.dll

[JetBrains.Annotations.UsedImplicitly]
internal static class IsExternalInit

Remarks

C# 9 introduced init-only setters, which allow properties to be set during object initialization but not afterward. The compiler requires the System.Runtime.CompilerServices.IsExternalInit type to exist in the assembly for this feature to work.

Unity's .NET Standard 2.1 profile does not include this type, so this empty static class acts as a polyfill. Its mere existence satisfies the compiler requirement — it contains no methods or fields.

How It Works

When the C# compiler encounters an init accessor:

public string Name { get; init; }

It generates IL that references System.Runtime.CompilerServices.IsExternalInit. If this type is missing, compilation fails with:

error CS0518: Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported

This polyfill class provides the type, enabling init syntax throughout the Paragon codebase.

Why internal

The class is internal to prevent it from being visible to other assemblies, which might define their own polyfill. The [UsedImplicitly] attribute suppresses ReSharper/Rider warnings about the class appearing unused.

Quick Lookup

Goal	How
Use init properties	Just write { get; init; } — this polyfill makes it work
Prerequisite	None — simply having this file in the project is sufficient

Common Pitfalls

No action required This class is a compile-time polyfill. You never need to reference, instantiate, or interact with it. If you see it in the codebase, leave it as-is.

Do not make it public Making this class public can cause conflicts if other assemblies (e.g., third-party packages) define their own IsExternalInit polyfill, resulting in duplicate type errors.

Examples

Using init-only Properties

With this polyfill in the project, init accessors work as expected:

public class PlayerData
{
    public string Name { get; init; }
    public int Level { get; init; }
}

// Valid — initialization
var data = new PlayerData { Name = "Hero", Level = 1 };

// Invalid — compile error: init-only property
// data.Name = "Villain";

Records and init

init accessors also enable record types and with expressions:

public record struct Coordinate(float X, float Y);

var a = new Coordinate(1f, 2f);
var b = a with { X = 3f }; // Creates a copy with modified X

See Also

• LowLevel Overview — system overview

• PlayerLoopInjector — the other low-level utility