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Page Revision: Wed, May 04, 2022, 9:36 AM

using System;
using System.Linq.Expressions;

public static class LinqExtensions
{
    /* Adapted from
        * https://stackoverflow.com/questions/29565373/combine-listexpressionfunct-bool-to-an-or-clause-linq
        */
    public static Expression<Func<T, bool>> OrElse<T>(
        this Expression<Func<T, bool>> a,
        Expression<Func<T, bool>> b)
    {
        var bodyB = b.Body.Replace(b.Parameters[0], a.Parameters[0]);

        return Expression.Lambda<Func<T, bool>>(Expression.OrElse(a.Body, bodyB), a.Parameters);
    }


    private static Expression Replace(this Expression expression, Expression searchEx, Expression replaceEx)
    {
        return new ReplaceVisitor(searchEx, replaceEx).Visit(expression);
    }


    private class ReplaceVisitor : ExpressionVisitor
    {
        private readonly Expression _from, _to;
        public ReplaceVisitor(Expression from, Expression to)
        {
            _from = from;
            _to = to;
        }
        public override Expression Visit(Expression node)
        {
            return node == _from ? _to : base.Visit(node);
        }
    }
}