Get default case class arguments via Shapeless
2
Does shapeless provide a type class/macro that summons a HList containing the default values for all parameters of a case class?
Let's say we have this case class:
case class User(name: String, age: Int = 18)
Then I would like to get such a HList:
None :: Some(() => 18) :: HNil
scala shapeless
asked Nov 23 '18 at 21:31
AkiAki
1,098212
add a comment |
2
Does shapeless provide a type class/macro that summons a HList containing the default values for all parameters of a case class?
Let's say we have this case class:
case class User(name: String, age: Int = 18)
Then I would like to get such a HList:
None :: Some(() => 18) :: HNil
scala shapeless
asked Nov 23 '18 at 21:31
AkiAki
1,098212
add a comment |
2
2
2
1
Does shapeless provide a type class/macro that summons a HList containing the default values for all parameters of a case class?
Let's say we have this case class:
case class User(name: String, age: Int = 18)
Then I would like to get such a HList:
None :: Some(() => 18) :: HNil
scala shapeless
asked Nov 23 '18 at 21:31
AkiAki
1,098212
Does shapeless provide a type class/macro that summons a HList containing the default values for all parameters of a case class?
Let's say we have this case class:
case class User(name: String, age: Int = 18)
Then I would like to get such a HList:
None :: Some(() => 18) :: HNil
scala shapeless
scala shapeless
asked Nov 23 '18 at 21:31
AkiAki
1,098212
asked Nov 23 '18 at 21:31
AkiAki
1,098212
asked Nov 23 '18 at 21:31
AkiAki
1,098212
asked Nov 23 '18 at 21:31
AkiAki
1,098212
asked Nov 23 '18 at 21:31
AkiAki
1,098212
1,098212
add a comment |
add a comment |
1 Answer
1
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6
Default parameters is implemented over synthetic methods.
Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala
import shapeless.Default
case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())
Out:
None :: Some(18) :: HNil
answered Nov 23 '18 at 23:28
fshpfshp
1765
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
6
Default parameters is implemented over synthetic methods.
Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala
import shapeless.Default
case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())
Out:
None :: Some(18) :: HNil
answered Nov 23 '18 at 23:28
fshpfshp
1765
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
add a comment |
6
Default parameters is implemented over synthetic methods.
Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala
import shapeless.Default
case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())
Out:
None :: Some(18) :: HNil
answered Nov 23 '18 at 23:28
fshpfshp
1765
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
add a comment |
6
6
6
Default parameters is implemented over synthetic methods.
Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala
import shapeless.Default
case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())
Out:
None :: Some(18) :: HNil
answered Nov 23 '18 at 23:28
fshpfshp
1765
Default parameters is implemented over synthetic methods.
Try it trait. https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/default.scala
import shapeless.Default
case class User(name: String, age: Int = 18)
val d = Default[User]
println(d())
Out:
None :: Some(18) :: HNil
answered Nov 23 '18 at 23:28
fshpfshp
1765
edited Nov 24 '18 at 0:53
answered Nov 23 '18 at 23:28
fshpfshp
1765
answered Nov 23 '18 at 23:28
fshpfshp
1765
answered Nov 23 '18 at 23:28
fshpfshp
1765
1765
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
add a comment |
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
Default values get compiled to methods that produce the value. In my example scala would create a method that returns 18. I thought shapeless may provide references to those methods. I've tried to implement such a macro on my own but I did not find an api that allows the macro writer to somehow get those generated methods even though it should theoretically be possible...
– Aki
Nov 23 '18 at 23:43
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
@Aki use it github.com/milessabin/shapeless/blob/master/core/src/main/scala/…
– fshp
Nov 24 '18 at 0:35
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
That seems to be what i was looking for. May you write that as a separate answer so I could accept it?
– Aki
Nov 24 '18 at 10:34
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
@Aki I updated the answer
– fshp
Nov 24 '18 at 19:57
add a comment |
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