Hi I have a styling question related to data classes and cop

Question

Hi I have a styling question related to data classes and copy method ``` val connectionUri = jdbc postgresql $host $port $database user=$username amp password=$password val connection = PostgreSQLConnectionBuilder createConnectionPool connectionUri it copy connectionCreateTimeout = 1 ``` I am writing a lib and I want to configure a connection Configuration is a data class and all are vals Can I avoid the `it copy` in the code above call the copy somehow in the lib or is there an apply method

oshai · Answer

Connection configuration is something like this

oshai · Answer

``` data class ConnectionPoolConfiguration JvmOverloads constructor val host String = localhost val port Int = 5432 val database String = null val username String = dbuser val password String = null val connectionCreateTimeout Long = null ```

oshai · Answer

so I cannot mutate it that is why I am using the `it copy`

oshai · Answer

do you think of another alternative

diesieben07 · Answer

`copy` is the right tool here Why don t you want to use it

oshai · Answer

just to make it a nicer DSL

diesieben07 · Answer

If you want a nice DSL you d have to write something with actual `var`s if you want regular assignments

oshai · Answer

I like the configuration to be immutable

oshai · Answer

I wish to somehow call copy from the lib on parameters I get from the user thinking face

diesieben07 · Answer

Can you show what kind of syntax you want

oshai · Answer

``` PostgreSQLConnectionBuilder createConnectionPool connectionUri connectionCreateTimeout = 1 ```

oshai · Answer

to override specific values

diesieben07 · Answer

You must have a `var` somewhere to achieve that syntax It doesn t have to be in the actual connection properties you can have a temporary mutable object

diesieben07 · Answer

But what s wrong with ``` PostgreSQLConnectionBuilder createConnectionPool connectionUri ConnectionProperties createTimeout = 1 ```

oshai · Answer

the first part `PostgreSQLConnectionBuilder createConnectionPool connectionUri ` is building a default configuration and I would like to be able to override some of the properties later so I need to use that object

Nikky · Answer

you could use a mutable variant of the ConnectionPool in the lambda but then make it immutable and return that

oshai · Answer

is there a simple way to do that without cloning the class

diegog · Answer

Could you please post the signature of `createConnectionPool`

diegog · Answer

I totally agree copying doesn t feel great

oshai · Answer

it looks like that ``` JvmStatic fun createConnectionPool url String configurator ConnectionPoolConfiguration gt ConnectionPoolConfiguration = it ConnectionPool lt MySQLConnection gt val configuration = URLParser parseOrDie url val connectionPoolConfiguration = configurator with configuration ConnectionPoolConfiguration username = username host = host port = port password = password database = database ssl = ssl charset = charset maximumMessageSize = maximumMessageSize allocator = allocator queryTimeout = queryTimeout toMillis return ConnectionPool MySQLConnectionFactory connectionPoolConfiguration connectionConfiguration connectionPoolConfiguration poolConfiguration connectionPoolConfiguration executionContext ```

diegog · Answer

Even if it may feel a bit more fiddly I would pass just ConnectionPoolConfiguration as a parameter forcing the caller to build the object as it needs I ve seen may times using it copy in a way that feels dealing with mutable objects As an end user of the library I would like to be in control and pass the configuration in grinning It would be great if someone else can come up with a better solution

dave08 · Answer

I think provide overloads of createConnectionPool function with the most common things a user might want to set and if they need more flexibility just pass in the configuration object If it wouldn t need java interop you could always have defaults for all the function params and let the user choose what to provide < oshai>

dave08 · Answer

Behind the scenes the overloads create the immutable configuration onject with sensible defaults

oshai · Answer

Can you give an example

dave08 · Answer

Another possibility is to have a builder class like But what I meant previously was something like this except that you can have an overload to just provide the whole config object or you could make it mutable like Ktor I think the second is better because most of your configs are going to be supplied in most cases database user password host port can maybe be guessed by implementation 3306 mysql 5431 postgres but should optionally be provided the rest could have reasonable defaults or be provided with config object < oshai>

oshai · Answer

a builder is a valid option altough I thought we don t need that anymore with kotlin wink