C# Expression Parser for Unity3D

License: Other

Language: C#

Keywords: ast, eval, expression-evaluator, expression-parser, unity, unity-asset, unity-scripts, unity3d, unity3d-plugin

Build Status


Attention! This is a paid package, you can use it anywhere if you purchased it.

This package provides the API for parsing and expression execution written in C#. It is specially designed to work with the Unity on various platforms. Since it is written in C# 3.5 and has no additional dependencies, it should work with any version of Unity (and .NET framework).

It is tested to work on:

  • IOS
  • Android
  • WebGL
  • PC/Mac

It should work on any other platforms. For AOT execution platforms (iOS, WebGL) a link.xml should be added to project's root directory. Read more about IL code stripping in official documentation.


  • CSharpExpression
    • Evaluate
    • Parse
  • AotCompilation
    • RegisterFunc
    • RegisterForFastCall (optional stuff)


Parsing C# expression into System.Linq.Expression.Expression[T]:

var mathExpr = "Math.Max(x, y)";
var exprTree = CSharpExpression.Parse<double, double, double>(mathExpr, arg1Name: "x", arg2Name: "y") 
// exprTree -> Expression<Func<double, double, double>>

Evaluating C# expression:

var arifExpr = "2 * (2 + 3) << 1 + 1 & 7 | 25 ^ 10";
var result = CSharpExpression.Evaluate<int>(arifExpr); 
// result -> 19


The parser recognizes the C# 4 grammar only. It includes:

Nullable types are supported. Generics are supported. Enumerations are supported. Type inference is not available and your should always specify generic parameters on types and methods.

Known Types

For security reasons the parser does not provide access to any types except:

  • argument types
  • primitive types
  • Math, Array, Func<> (up to 4 arguments) types

To access other types your should pass typeResolver parameter in Parse and Evaluate method:

var typeResolver = new KnownTypeResolver(typeof(Mathf), typeof(Time));
CSharpExpression.Evaluate<int>("Mathf.Clamp(Time.time, 1.0f, 3.0f)", typeResolver); 

If you want to access all types in UnityEngine you can pass custom AssemblyTypeResolver as typeResolver parameter.

var typeResolver = new AssemblyTypeResolver(typeof(UnityEngine.Application).Assembly);

For security reasons any member invocation on System.Type will throw exceptions until System.Type is added as known type.

AOT Execution

You can compile and evaluate expression created by System.Linq.Expression and execute it in AOT environment where it is usually impossible.

var expr = (Expression<Func<Vector3>>)(() => new Vector3(1.0f, 1.0f, 1.0f));
var fn = expr.CompileAot();

fn; // -> Func<Vector3>
fn(); // -> Vector3(1.0f, 1.0f, 1.0f)

iOS, WebGL and most console platforms use AOT compilation which imposes following restrictions on the dynamic code execution:

  • only Expression<Func<...>> could be used with CompileAot() and Lambda types
  • only static methods using primitives (int, float, string, object ...) are optimized for fast calls
  • all used classes/methods/properties should be visible to Unity's static code analyser
  • An additional preparation should be made for AOT execution platforms. This link.xml should be added in project's root folder. Read more about IL code stripping in official documentation.

See Also

WebGL and iOS

  • Only Func<> (up to 4 arguments) Lambdas are supported
  • Instance methods invocation performs slowly due reflection
  • Moderate boxing for value types (see roadmap)

You can ensure that your generic Func<> pass AOT compilation by registering it with AotCompilation.RegisterFunc

AotCompilation.RegisterFunc<int, bool>(); // will enable Func<int, bool> lambdas anywhere in expressions

Improving Performance

You can improve the performance of methods invocation by registering their signatures in AotCompilation.RegisterForFastCall().

// Supports up to 3 arguments.
// First generic argument is your class type.
// Last generic argument is return type.

AotCompilation.RegisterForFastCall<InstanceT, ResultT>()
AotCompilation.RegisterForFastCall<InstanceT, Arg1T, ResultT>()
AotCompilation.RegisterForFastCall<InstanceT, Arg1T, Arg2T, ResultT>()
AotCompilation.RegisterForFastCall<InstanceT, Arg1T, Arg2T, Arg3T, ResultT>()


public class MyVectorMath
    public Vector4 Dot(Vector4 vector, Vector4 vector);
    public Vector4 Cross(Vector4 vector, Vector4 vector);
    public Vector4 Scale(Vector4 vector, float scale);    

// register Dot and Cross method signatures
AotCompilation.RegisterForFastCall<MyVectorMath, Vector4, Vector4, Vector4>();
// register Scale method signature
AotCompilation.RegisterForFastCall<MyVectorMath, Vector4, float, Vector4>();


You can send suggestions at

  • Expression serialization (in-progress)
  • Void expressions (System.Action delegates) (done)
  • Parser: Delegate construction from method reference
  • Parser: Type inference for generics
  • Parser: Full C#6 syntax
  • Parser: Extension methods
  • Parser: Type initializers, List initializers
  • Custom editor with auto-completion for Unity



changed order or SyntaxTreeNode fields and added "original C# expression" field to parsed AST. refactored C# expression rendering to support null-propagation expressions, type aliases (int, byte, object ...), renamed "Render" methods to "FormatAsCSharp". Now it is "formatting" moved c# "formatting" methods to CSharpExpression class mark old "Parse" functions as errors mark old "Render" methods as obsolete renamed CSharpExpressionFormatter to CSharpExpressionFormatter fixed indexer experssion rendering refactored NameUtils to properly render C# type names


renamed ParseTreeNode.Lexeme to .Token renamed few member of TokenType for better clarity added documentation file in Unity project assets changed 'propertyOrFieldName' attribute to 'name' in SyntaxTreeNode renamed PropertyOfFieldBinder to MemberBinder changed 'PropertyOrField' expression type to 'MemberResolve' in SyntaxTreeNode added backward compatibility checks in all related classes


  • added protection against wrong expressions like 'a b' which later bound as 'b'
  • fixed some tokenization errors:
    • 'issa'scanned as 'is'[Operator] and 'sa'[Identifier], now as 'issa'
    • '.09' scanned as '.'[Operator] and '09'[Number], now as '0.09'
    • '0.1x' scanned as '0.1'[Number] and 'x'[Identifier], now cause error
  • added method calls on numbers (example 1.ToString())
  • added short number notation (example '.9' for '0.9')
  • added '@' prefix for identifiers (example '@is')
  • done small Tokenizer optimization (reduced string allocation during scanning)


  • added ExpressionPacker type. This type allows packing/unpacking expressions into primitive structures (Dictionaries, Arrays...). These structures could be serialized and wired by network or stored for future use.
  • added better error message for some binding cases
  • denying call to 'Type.InvokeMember' if 'Type' is not within 'known types'.


  • fixed conditional operator (a ? b : c) parsing with method call in place of 'b'


  • fixed IL2CPP compilation error due _Attribute interface complilation failure
  • added few interfaces to AOT.cs file for better AOT coverage



  • added support for void expressions (Action<> delegates)
  • added support of '.NET Standart 1.3' and '.NET Core 2.0' platforms


  • Release version, no actual changes except



  • added more descriptive message for member binding error
  • added autodoc comments for public members
  • hid ReadOnlyDictionary from public access
  • removed Unity WebGL #if for unsigned types. Unity's bug was fixed.
  • added support for generic types and generic methods
  • added nullable types and ? suffix support
CSharpExpression.Evaluate<int?>("default(int?)"); // -> null
  • added lambda expressions. Syntax is () => x and new Func(a => x)
  • added support for expression's parameter re-mapping with lambda expression syntax:
CSharpExpression.Evaluate<int, int, int>("(x,y) => x + y", 2, 2); // -> 4
  • added support for Func<> lambdas for AOT environments
  • added additional constructor to Binder class
public Binder(Type lambdaType, ITypeResolver typeResolver = null);
  • added ArgumentsTree.ToString() method
  • added aliases for build-in types. Aliases resolved during binding phase inside Binder.Bind() method.


  • fixed error with wrongly resolved types (only by name) in KnownTypeResolver
  • fixed bug with ACCESS_VIOLATION on iOS (Unity 5.x.x IL2CPP)
  • fixed few Unity 3.4 related errors in code
  • fixed 'new' expression parsed with error on chained calls new a().b().c()
  • fixed some cases of lifted binary/unary/conversion operations
  • fixed some AOT'ed operations on System.Boolean type
  • fixed null-propagation chains generate invalid code
  • fixed some edge cases of resolving nested generic types
  • fixed error with types without type.FullName value
  • fixed Condition operator types promotion
  • fixed Power operator types promotion and null-lifting
  • fixed enum constants threated as underlying types during binary/unary operations

Breaking changes in 2.0

  • ParserNode renamed to ParseTreeNode
  • ExpressionTree renamed to SyntaxTreeNode
  • ExpressionBuilder renamed to Binder
  • ITypeResolutionService renamed to ITypeResolver
  • ITypeResolver.GetType removed
  • ITypeResolver now could be configured with TypeDiscoveryOptions

  • fixed error them creating nullable types via "new" keyword
  • fixed Embedded Resource addressing problem on IL2CPP WebGL (localized error messages)
  • fixed some cases of nullable types binding
  • fixed Enum member resolution
  • added Power(**) operator into C# syntax
CSharpExpression.Evaluate<int>("2 ** 2"); // -> 4
  • added TypeResolutionService chaining for better KnownTypes re-use

  • fixed error with nulled constants after first call for AOT-ted expression.
  • added ToString() impl for ExpressionTree

  • added Null-conditional Operators (example: a.?b.?.c)
  • fixed array indexing expressions
  • added array types support in type expressions ('convert', 'typeof', 'is' etc.)



Install-Package GameDevWare.Dynamic.Expressions


Package at Unity Asset Store


Please send any questions at


If you embed this package, you must provide a link and warning about embedded C# Eval() for your customers in the description of your package. If your package is free, they could use embedded C# Eval() free of charge. In either case, they must acquire this package from Unity Store.

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Project Statistics

Sourcerank 6
Repository Size 1.43 MB
Stars 67
Forks 10
Watchers 12
Open issues 3
Dependencies 0
Contributors 1
Tags 6
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Packages Referencing this Repo

C# expression parsing and execution library. Designed for AOT runtimes (Unity's IL2CPP, .NET Nat...
Latest release 2.2.6 - Updated - 67 stars

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2.1.2 March 17, 2017
2.1.0-alpha March 10, 2017
2.0.0-alpha February 08, 2017 January 13, 2017 January 13, 2017 January 13, 2017

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