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ExpressionCompiler

Compiles C# expression strings into strongly-typed delegates. Results are cached for reuse.

public class ExpressionCompiler

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Constructor

public ExpressionCompiler(int maxCompilesBeforeRecycle = 1000)

Parameter	Description
maxCompilesBeforeRecycle	Maximum unique compilations before the internal AssemblyLoadContext is unloaded and recreated. Set to 0 for no limit.

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Methods

Compile<TDelegate>(string expression, string[] parameterNames, string[]? additionalNamespaces, AssemblyReferenceProvider? referenceProvider)

Compiles a C# expression into a typed delegate.

var compiler = new ExpressionCompiler();
var del = compiler.Compile<Func<int, bool>>(
    "x > 0",
    new[] { "x" }
);
bool result = del(42);  // true

Parameters:

• expression — C# expression body
• parameterNames — Ordered names matching delegate signature
• additionalNamespaces — Extra using namespaces (e.g., "Demo.Models")
• referenceProvider — Custom assembly whitelist for sandboxing (optional)

Unload()

Forces immediate unload of the current AssemblyLoadContext and clears the delegate cache.

compiler.Unload();  // Reclaim memory

CompileCount

Returns the number of unique compilations performed.

Console.WriteLine($"Compilations: {compiler.CompileCount}");

CurrentContextName

Returns the current AssemblyLoadContext name for diagnostics.

Console.WriteLine($"Context: {compiler.CurrentContextName}");

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ALC Recycling

Each compilation loads a new assembly into a collectible AssemblyLoadContext. To prevent memory growth:

Strategy	When
Automatic recycling	Set maxCompilesBeforeRecycle (default: 1000)
Manual unload	Call Unload() when memory pressure detected
Reuse delegates	The compiler caches delegates by expression signature

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Sandboxing

Use AssemblyReferenceProvider to restrict which assemblies are available to compiled expressions.

var whitelist = new AssemblyReferenceProvider();
// Only allow specific assemblies
var del = compiler.Compile<Func<Customer, bool>>(
    "customer.Name.Length > 0",
    new[] { "customer" },
    referenceProvider: whitelist
);

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AOT/Trimming

Reflection-heavy methods are annotated with [RequiresUnreferencedCode]. For trimmed apps:

<ItemGroup>
  <TrimmerRootAssembly Include="RoslynRules" />
</ItemGroup>

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Related

• Delegate Types — Supported signatures
• AssemblyReferenceProvider — Sandboxing