JJ.Framework.PlatformCompatibility.Core 4.5.6073

JJ.Framework.PlatformCompatibility.Core

Shims that mimic new features for old .NETs, so new code can compile for older tech.
It's internal tooling in support of the JJ projects and only supports a limited selection.

Background

When you want a single code base to compile on both old and new .NETs, you run into trouble. Things like init, required and nullability attributes: they just aren't there on older targets.

These shims step in silently: on platforms that already have the real thing, they stay out of the way. On older ones, they provide just enough so the compiler stops complaining. Sometimes the behavior may be a no-op, but at least it compiles and things keep working.

The following shims have been added:

Argument Checks

Newer .NETs added shorthand throws which aren't there yet in some older .NET versions:

• ThrowIfNull
• ThrowIfNullOrWhiteSpace

Language Features

A few language keywords that older .NET versions don't support without a stub somewhere:

• [RequiredMember] - needed for the required keyword on older targets.
• [CallerArgumentExpression] - needed to extract the text of the expression of how the argument is passed.
• [OverloadResolutionPriority] - hints to the compiler which overload to prefer, when there's ambiguity.
• IsExternalInit - needed for init-only setters.
• [CompilerFeatureRequired] - lets a type signal it relies on a specific compiler feature.

Nullability

Nullability attributes might be missing on older platforms:

• [NotNull] - tells the compiler a value won't come out null.
• [NotNullWhen] - same, but only when the method returns a particular Boolean value.

As PlatformCompatibility.Core makes sure they're there, the compiler knows what to do with them, and the nullability intents are used, even for older .NET versions.

Trimming / AOT

When publishing with trimming or native compilation (AOT), the compiler needs hints about what to keep. These attributes carry those hints. On platforms that don't know them yet, the shims provide the same code at least compiles:

• [DynamicallyAccessedMembers]
• [DynamicallyAccessedMemberTypes]
• [DynamicDependency]
• [RequiresUnreferencedCode]
• [RequiresDynamicCode]
• [UnconditionalSuppressMessage]

Threading

• Lock - a new type introduced for more efficient locking, backported so the same locking pattern compiles on older targets.

Utilities

• HashCode - HashCode.Combine(...) for older .NET versions that don't have it built in.

Release Notes

2026-04-04 | 4.4/0.252 : Initial

• Run new code on older .NETs
• Shims for argument checks, language features, nullability, trimming/AOT, threading and hash codes
• Full test coverage and member docs

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