Allow scanning rows to interface{} type

[usrlocl]

I would like to be able to specify interface{} types for Scan as so,

var col1 interface{}
conn.QueryRow(ctx, "SELECT foo FROM bar").Scan(&col1)

However, it throws the following error

converting String to *interface {} is unsupported

Doing this can allow for some generic behaviour when the column types are not known in the application.

It should be a straight forward change. Wondering if it was a conscious choice to not allow this or would you be open for a pull request?

[kshvakov]

You can make columns on the fly like this https://github.com/ClickHouse/clickhouse-go/blob/master/tests/issues/476/main.go#L47.

[usrlocl]

Is this available only on the standard interface? Is there an equivalent on the native interface as well, or any plans to introduce?

[kshvakov]

I'll add ColumnTypes to native interface

[usrlocl]

Great! Btw, what are the plans with respect to standard vs native interfaces? Will they be maintained in conjunction going forward or is one likely to be deprecated?
Also interested to know if it's mainly performance reason to prefer native one or are there other limitations with standard one?

[kshvakov]

We will support both interfaces, since in some cases users are more accustomed to using the standard interface. In the native interface, we can choose the names of methods and their meaning is clear, while in the standard one everything may not be so obvious. For example, we use "transactions" to prepare a block with data, while the native interface has a method called PrepareBatch, the same with asynchronous requests, and so on

[kshvakov]

Done d214e35

[usrlocl]

I tried this on HEAD. I can use ColumnTypes() now but getting the same error as before with native interface.

 [ScanRow]: (type) converting Enum8 to *interface {} is unsupported

I think the issue is that ScanRow still sees the type as *interface{} which has no handling. I modified the code you shared to use native interface.

[kshvakov]

I have added an example 9b480b5

[usrlocl]

Ah, it works with reflect.Value instead of pointer type. This should be good as well.

Thank you very much for the change and all the help!