LinqExpressions.cs

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Linq.Expressions;

namespace System.Linq.Expressions
{
    public static class LinqExpressionsExtensions
    {
        public static MemberInfo GetMemberInfo<T, U>(this Expression<Func<T, U>> expression)
        {
            var member = expression.Body as MemberExpression;
            if (member != null)
                return member.Member;

            throw new ArgumentException("Expression is not a member access", "expression");
        }


        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> a, Expression<Func<T, bool>> b)
        {

            ParameterExpression p = a.Parameters[0];

            SubstExpressionVisitor visitor = new SubstExpressionVisitor();
            visitor.subst[b.Parameters[0]] = p;

            Expression body = Expression.AndAlso(a.Body, visitor.Visit(b.Body));
            return Expression.Lambda<Func<T, bool>>(body, p);
        }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> a, Expression<Func<T, bool>> b)
        {

            ParameterExpression p = a.Parameters[0];

            SubstExpressionVisitor visitor = new SubstExpressionVisitor();
            visitor.subst[b.Parameters[0]] = p;

            Expression body = Expression.OrElse(a.Body, visitor.Visit(b.Body));
            return Expression.Lambda<Func<T, bool>>(body, p);
        }

        internal class SubstExpressionVisitor : System.Linq.Expressions.ExpressionVisitor
        {
            public Dictionary<Expression, Expression> subst = new Dictionary<Expression, Expression>();

            protected override Expression VisitParameter(ParameterExpression node)
            {
                Expression newValue;
                if (subst.TryGetValue(node, out newValue))
                {
                    return newValue;
                }
                return node;
            }
        }

    }
}