Dynamic Generic Types as Method<T...>

[sgf]

how about add this new Feature(syntax) like:

public List<T..> ExeSql<T..>(string sql,params object[] objs)
{
var len=length(T..);
typeof(T..[0])
typeof(T..[1])
typeof(T..[2])
...
..
..
//or maybe use foreach
foreach(typeof(T) t in T..)
{
      t....
}


}

to instead of

public List<T1> ExeSql <T1> (string sql,params object[] objs)
public List<T1,T2> ExeSql<T1,T2>(string sql,params object[] objs)
public List<T1,T2,T3> ExeSql<T1,T2,T3>(string sql,params object[] objs)
<T1,T2,T3,T4>...
<T1,T2,T3,T4,T5>...
T6...
...
...
..

[svick]

This looks like a duplicate of dotnet/roslyn#5058, which was closed with this message:

I am not moving this particular issue [from dotnet/roslyn to dotnet/csharplang] because I don't have confidence that the LDM would likely consider doing this as proposed. I think we might consider doing something along these lines along with higher-kinded types if we do that; see #339.

[bondsbw]

What is List<T1,T2> and List<T1,T2,T3>?

Where would this be useful?

[svick]

@bondsbw I think it's effectively List<(T1, T2, T3)>. So, if you want to return a table with a person's name and age, you would have something like ExeSql<string, int>("select name, age from people").

[bondsbw]

var items = ExeSql<(string, int)>("select name, age from people");
(string name, int age) = items[0];

Since that is legal today with a single type parameter, I'm not seeing anything very useful in this proposal.

[sgf]

@bondsbw
where if u want to design a API to return multi Result Types
such call like:

 Tuple<List<Account>,List<User>,List<UserInfo>,List<UserSetting>> ExeSql<Account,User,UserInfo,UserSetting>(.....);

 Tuple<List<Account>,List<User>,List<UserInfo>,List<UserSetting>.....{or more types result}>ExeSql<Account,User,UserInfo,UserSetting,.....{or more types result}>(.....);

u should be define lots of overload Methods.

but if we can just define once time.thats will be Write less code,yes,we just need write once in One Method.

[sgf]

@bondsbw
sorry my project is very old
let me try whats ur submit(use new Tuple syntax ).
if i can define like thats,i will close this issues

[sgf]

@bondsbw
these codes could be Compiled

        public class TestClass {

        }

        public List<T> TestMethod<T>(){


            return new List<T>();
        } 

            Test<(string, int, TestClass)>();

but how can i get the Types from T with argument of Tuple in TestMethod ?

because I needed to construct the types objects to return;

[sgf]

i found it GetGenericArguments. @bondsbw thank u,and thanks to all.

public  class Program
    {
        public class TestClass
        {
        }
        public static List<T> Test<T>()
        {
            var types = typeof(T).GetGenericArguments().ToList();
            types.ForEach(t => Console.WriteLine(t.Name));
            return new List<T>();
        }
        static void Main(string[] args)
        {
            Test<(string, int, TestClass)>();
            Console.ReadKey();
        }
    }