The best use case of dynamic type variables for me was when, recently, I was writing a data access layer in ADO.NET (using SQLDataReader) and the code was invoking the already written legacy stored procedures. There are hundreds of those legacy stored procedures containing bulk of the business logic. My data access layer needed to return some sort of structured data to the business logic layer, C# based, to do some manipulations (although there are almost none). Every stored procedure returns different set of data (table columns). So instead of creating dozens of classes or structs to hold the returned data and pass it to the BLL, I wrote the below code which looks quite elegant and neat.

public static dynamic GetSomeData(ParameterDTO dto)
        {
            dynamic result = null;
            string SPName = "a_legacy_stored_procedure";
            using (SqlConnection connection = new SqlConnection("my connection string"))
            {
                SqlCommand command = new SqlCommand(SPName, connection);
                command.CommandType = System.Data.CommandType.StoredProcedure;                
                command.Parameters.Add(new SqlParameter("@empid", dto.EmpID));
                command.Parameters.Add(new SqlParameter("@deptid", dto.DeptID));
                connection.Open();
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        dynamic row = new ExpandoObject();
                        row.EmpName = reader["EmpFullName"].ToString();
                        row.DeptName = reader["DeptName"].ToString();
                        row.AnotherColumn = reader["AnotherColumn"].ToString();                        
                        result = row;
                    }
                }
            }
            return result;
        }

COM互操作。尤其是IUnknown。这是专门为它设计的。

你可以使用pythonnet调用动态语言，比如CPython:

充满活力。

在对泛型应用数值运算符时，可以将泛型强制转换为动态泛型。这提供了类型安全性并避免了泛型的限制。这本质上是*鸭子打字:

T y = x *(动态)x，其中typeof(x)为T

它在运行时求值，所以你可以像在JavaScript中那样切换类型到你想要的任何类型。这是正确的:

dynamic i = 12;
i = "text";

所以你可以根据需要改变类型。把它作为最后的手段;这是有益的，但我听说在生成IL的场景下发生了很多事情，这可能以性能代价为代价。

The best use case of dynamic type variables for me was when, recently, I was writing a data access layer in ADO.NET (using SQLDataReader) and the code was invoking the already written legacy stored procedures. There are hundreds of those legacy stored procedures containing bulk of the business logic. My data access layer needed to return some sort of structured data to the business logic layer, C# based, to do some manipulations (although there are almost none). Every stored procedure returns different set of data (table columns). So instead of creating dozens of classes or structs to hold the returned data and pass it to the BLL, I wrote the below code which looks quite elegant and neat.

public static dynamic GetSomeData(ParameterDTO dto)
        {
            dynamic result = null;
            string SPName = "a_legacy_stored_procedure";
            using (SqlConnection connection = new SqlConnection("my connection string"))
            {
                SqlCommand command = new SqlCommand(SPName, connection);
                command.CommandType = System.Data.CommandType.StoredProcedure;                
                command.Parameters.Add(new SqlParameter("@empid", dto.EmpID));
                command.Parameters.Add(new SqlParameter("@deptid", dto.DeptID));
                connection.Open();
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        dynamic row = new ExpandoObject();
                        row.EmpName = reader["EmpFullName"].ToString();
                        row.DeptName = reader["DeptName"].ToString();
                        row.AnotherColumn = reader["AnotherColumn"].ToString();                        
                        result = row;
                    }
                }
            }
            return result;
        }

用法示例:

你使用了许多具有共同属性'CreationDate'的类:

public class Contact
{
    // some properties

    public DateTime CreationDate { get; set; }        
}

public class Company
{
    // some properties

    public DateTime CreationDate { get; set; }
    
}

public class Opportunity
{
    // some properties

    public DateTime CreationDate { get; set; }
    
}

如果你写一个通用的方法来检索'CreationDate'属性的值，你必须使用反射:

static DateTime RetrieveValueOfCreationDate(Object item)
{
    return (DateTime)item.GetType().GetProperty("CreationDate").GetValue(item);
}

使用“动态”概念，你的代码会更加优雅:

static DateTime RetrieveValueOfCreationDate(dynamic item)
{
    return item.CreationDate;
}