Processing, Compilation, and Execution of Expression Trees at Runtime

C# provides the ability to write lambda expressions such as n => n / 2. The right hand of such an expression can be processed at runtime. This project provides tools for such processing.

Features

• Comparison of expressions based on their structure
• Fast evaluation of expression trees without leaking memory
  • Interpretation
  • Cached Compilation
• Partial Evaluation
• Combining expressions via inlining
• Extraction of constants
• Substitution of parameters

NuGet

ExpressionUtils is distributed via NuGet to make it easier to embed into your project. The package name is 'MiaPlaza.ExpressionUtils'.

Examples

Some motivating examples to show the library functions:

Comparison

Expression<Func<int, bool>> isEvenExpression = x => x % 2 == 0;
Expression<Func<int, bool>> isEvenExpression2 = x => x % 2 == 0;

Console.Write(isEvenExpression == isEvenExpression2); // false
Console.Write(isEvenExpression.StructuralIdentical(isEvenExpression2)); // true

Expression<Func<int, bool>> isUnevenExpression = x => x % 2 == 1;

Console.Write(isEvenExpression.StructuralIdentical(isUnevenExpression, ignoreConstantValues: true)); // true

Evaluation

Expression<Func<int, bool>> isEvenExpression = x => x % 2 == 0;

var isEvenDelegate = CachedExpressionCompiler.Instance.CachedCompileLambda(isEvenExpression);

Console.Write(isEvenDelegate(5)); // false

Partial Evaluation

This collapses all subtrees to constants that are independent from the expression's parameters. This also removes closures and references.

int modul = 0;
Expression<Func<int, bool>> modulExpression = x => x % modul == 0;

modul = 2;
var isMultipleOfTwoExpression = PartialEvaluator.PartialEvalBody(
    modulExpression,
    ExpressionInterpreter.Instance);

Expression<Func<int, bool>> isEvenExpression = x => x % 2 == 0;

Console.Write(isEvenExpression.StructuralIdentical(modulExpression)); // false
Console.Write(isEvenExpression.StructuralIdentical(isMultipleOfTwoExpression)); // true

modul = 3;
var isMultipleOfThreeExpression = PartialEvaluator.PartialEvalBody(
    modulExpression,
    ExpressionInterpreter.Instance);

Console.Write(isEvenExpression.StructuralIdentical(isMultipleOfThreeExpression)); // false

Maintainer's Notice

To create a new Release:

• bump the version numbers in the project file
• create a Release here on github
• dotnet pack -c Release
• cd ExpressionUtils/bin/Release/
• Create an API key for miaplaza at https://www.nuget.org/account/apikeys
• dotnet nuget push MiaPlaza.ExpressionUtils.….nupgk -k YOUR_KEY_HERE -s -s https://api.nuget.org/v3/index.json