How to implement a generic c# interface-CodePudding

I am having trouble understanding what my issue is here. CS0452 error, The type T must be ref type in order to use as a parameter...

The error is on this line: Response<T> tableEntity = TC.GetEntity<T>(pk, rk);

using Azure;
using Azure.Data.Tables;

namespace AzureDataTables
{
    public class AzureDataTables<T> : IAzureDataTables<T> where T : class, ITableEntity, new()
    {
        ITableEntity GetTableEntity(string pk, string rk);
    }

    public class AzureDataTables<T> : IAzureDataTables<T> where T : ITableEntity, new()
    {
        public T GetTableEntity(string pk, string rk)
        {
            var tableEntity = TC.GetEntity<T>(pk, rk);
            return tableEntity.Value;
        }
        public TableServiceClient TSC { get; set; } = new TableServiceClient("");
        public TableClient TC => TSC.GetTableClient("");
    }
}

CodePudding user response：

You need to use a concrete type in the implementation of the Interface if it has a generic type in it's contract. Here's a working example:

using Azure;
using Azure.Data.Tables;

namespace AzureDataTables
{
    public interface IAzureDataTables<T> where T : class, ITableEntity, new()
    {
        ITableEntity GetTableEntity(string pk, string rk);
    }

    public class AzureDataTables<T> : IAzureDataTables<T> where T : class, ITableEntity, new()
    {
        public ITableEntity GetTableEntity(string pk, string rk)
        {
            Response<T> tableEntity = TC.GetEntity<T>(pk, rk);
            return tableEntity.Value;
        }

        public TableServiceClient TSC { get; set; } = new TableServiceClient("");
        public TableClient TC => TSC.GetTableClient("");
    }
}

CodePudding user response：

TableClient.GetEntity<T>() has these constraints on the generic type:

where T : class, ITableEntity, new();

You're missing the class constraint on your own generic type as well to be able to use it with that function.

CodePudding user response：

The methode you are calling is TableClient.GetEntity this has a constraint where T : class, Azure.Data.Tables.ITableEntity, new();.
Your methode does not have the constraint class so when the compiler checks if your T can be used for the methode it does not comply with all the constraints.

If you change

public class AzureDataTables<T> : IAzureDataTables<T> where T : ITableEntity, new()

public class AzureDataTables<T> : IAzureDataTables<T> where T : class, ITableEntity, new()

It will compile.