.net5 Expression扩展

    public static class ExpressionEx
    {
        public static Expression> True() { return param => true; }
        public static Expression> False() { return param => false; }

        public static Expression> And(this Expression> one, Expression> another)
        {
            return one.Compose(another, Expression.AndAlso);
            //return one.Compose(another, Expression.And);
        }

        public static Expression> Or(this Expression> one, Expression> another)
        {
            //return one.Compose(another, Expression.OrElse);
            return one.Compose(another, Expression.Or);
        }

        public static Expression> Compose(this Expression> one, Expression> another, Func action)
        {
            //创建新参数
            var newParameter = Expression.Parameter(typeof(T));

            var parameterReplacer = new ParameterReplacer(newParameter);
            var left = parameterReplacer.Replace(one.Body);
            var right = parameterReplacer.Replace(another.Body);

            var body = action(left, right);

            return Expression.Lambda>(body, newParameter);
        }

        /// 

        /// 参数替换
        /// 
        internal class ParameterReplacer : ExpressionVisitor
        {
            public ParameterReplacer(ParameterExpression paramExpr)
            {
                Parameter = paramExpr;
            }

            //新的表达式参数
            private ParameterExpression Parameter { get; set; }

            public Expression Replace(Expression expr)
            {
                return this.Visit(expr);
            }

            /// 

            /// 覆盖父方法，返回新的参数
            /// 
            /// 
            /// 
            protected override Expression VisitParameter(ParameterExpression p)
            {
                return Parameter;
            }
        }
    }