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using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using Signum.Utilities;
using System.Reflection;
using Signum.Utilities.Reflection;
using Signum.Utilities.ExpressionTrees;
namespace Signum.Utilities.ExpressionTrees
{
/// <summary>
/// Evaluates & replaces sub-trees when first candidate is reached (top-down)
/// </summary>
public class ExpressionEvaluator : SimpleExpressionVisitor
{
HashSet<Expression> candidates;
private ExpressionEvaluator() { }
/// <summary>
/// Performs evaluation & replacement of independent sub-trees
/// </summary>
/// <param name="expression">The root of the expression tree.</param>
/// <param name="fnCanBeEvaluated">A function that decides whether a given expression node can be part of the local function.</param>
/// <returns>A new tree with sub-trees evaluated and replaced.</returns>
public static Expression PartialEval(Expression exp)
{
if (exp.NodeType == ExpressionType.Constant)
return exp;
var candidates = ExpressionNominator.Nominate(exp);
return new ExpressionEvaluator { candidates = candidates }.Visit(exp);
}
public static object Eval(Expression expression)
{
if (expression is ConstantExpression)
return ((ConstantExpression)expression).Value;
Delegate fn = Expression.Lambda(expression).Compile();
try
{
return fn.DynamicInvoke(null);
}
catch (TargetInvocationException ex)
{
Action savestack = Delegate.CreateDelegate(typeof(Action), ex.InnerException, "InternalPreserveStackTrace", false, false) as Action;
if (savestack != null)
savestack();
throw ex.InnerException;
}
}
protected override Expression Visit(Expression exp)
{
if (exp == null)
{
return null;
}
if (this.candidates.Contains(exp))
{
if (exp.NodeType == ExpressionType.Constant)
{
return exp;
}
return Visit(Expression.Constant(Eval(exp), exp.Type));
}
return base.Visit(exp);
}
}
}
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I'm Computer Scientist, one of the founders of Signum Software, and the lead developer behind Signum Framework.
www.signumframework.com
I love programming in C#, Linq, Compilers, Algorithms, Functional Programming, Computer Graphics, Maths...