how to understand the following scala call

Question

I have a quite puzzling question. I am playing with squeryl, and found when I used:

package models

import org.squeryl.{Schema, KeyedEntity}

object db extends Schema {
  val userTable = table[User]("User")

  on(userTable)(b => declare(
      b.email is(unique,indexed("idxEmailAddresses"))
      ))
}

I had to import import org.squeryl.PrimitiveTypeMode._

But this does not make sense to me. Here is is defined in org.squeryl.dsl.NonNumericalExpression, but why do I have to include the seemingly irrelevant import org.squeryl.PrimitiveTypeMode._?

Thank you.

probably because of an implicit conversion brought into scope. — kiritsuku, Apr 26 '13 at 18:24
don't know squeryl, thus can't say more than the code may look like `convert(b.email).is(...)` where `convert` is a member of `PrimitiveTypeMode`. Look into its sources, compare the types of all implicit methods and you will find your conversion. — kiritsuku, Apr 26 '13 at 18:36
I see from scala IDE that there is an implicit conversion from `b.email` => `string2ScalarString(b.email)`. But this `string2ScalarString` is not defined in `import org.squeryl.PrimitiveTypeMode._` — , Apr 26 '13 at 20:40
The IDE allows you to write out the implicit conversion explicitly and jump to its definition with hyperlinking. — kiritsuku, Apr 26 '13 at 22:05
Note: if you want, you can also include all needed implicit conversions separately. But I wouldn't do that, it's simpler to get them all... — VasiliNovikov, Apr 27 '13 at 09:23

cmbaxter · Accepted Answer · 2013-04-26T22:09:01.620

I agree with @sschaef that this is due to required implicit conversions. When APIs (like squeryl) decide to build a DSL (domain specific language) in order to get a slick looking way to code against their API, implicit conversions will be required. The core API probably takes certain types of objects that it might be cumbersome/ugly to be instantiating directly in the code. Thus, they will use implicit conversions to do some of the lifting for you and keep the DSL as clean as possible. If you check out the Scaladoc for the PrimitiveTypeMode object, you can see the many implicit defs that are defined on it. Implicit conversions (used in pimping libraries) will 'upconvert' from one type into another to gain access to more functionality on the pimped out class. When the code is the implicit things are explicitly included into the final compiled code.

http://squeryl.org/api/index.html#org.squeryl.PrimitiveTypeMode$

Also, I believe the implicit conversion you are looking for is:

import org.squeryl.PrimitiveTypeMode.string2ScalarString

which is inherited from org.squeryl.dsl.QueryDsl.

Thank you. Do you mind pointing out the exact implicit conversion it is doing here? — , Apr 26 '13 at 20:41

how to understand the following scala call

1 Answers1