scala command skips running main if class outside of singleton object -

edit: main method not called in scala script related (in particular, answer régis jean-gilles). post gives more details describe issue. , answer (by suish) give more practical demonstration explain behaviour of scala command.

content of miniscalaapp.scala

object miniscalaapp {   def main(args: array[string]) = {     println(s"scala version: ${scala.util.properties.scalaproporelse("version.number", "unknown")}")     println(new dinosaur("tyrannotitan", 4900))     println(new dinosaur("animantarx ", 300))   }    class dinosaur (name:string, weightkg: int) {     override def tostring = f"$name, weight: $weightkg kg"   } } 

executed @ command line by:

$ scala /myproject/src/main/scala/miniscalaapp.scala 

produces expected output:

scala version: 2.11.7
tyrannotitan, weight: 4900 kg
animantarx, weight: 300 kg

however, if dinosaur class placed outside of singleton object miniscalaapp scala command produces no console output, no error message.

object miniscalaapp {   def main(args: array[string]) = {     println(s"scala version: ${scala.util.properties.scalaproporelse("version.number", "unknown")}")     println(new dinosaur("tyrannotitan", 4900))     println(new dinosaur("animantarx ", 300))   } }  class dinosaur (name:string, weightkg: int) {   override def tostring = f"$name, weight: $weightkg kg" } 

in 2nd version, console output, code must compiled first , run miniscalaapp.class separately

$ scalac /myproject/src/main/scala/miniscalaapp.scala $ scala miniscalaapp 

question: reason scala command treats code differently?

scala -help explains all.

a file argument run scala script unless contains self-contained compilation units (classes , objects) , 1 runnable main method. in case file compiled , main method invoked. provides bridge between scripts , standard scala source.

so latter case defining object , class, run code script. in way say, same as...

scala> :paste // entering paste mode (ctrl-d finish)  object miniscalaapp {   def main(args: array[string]) = {     println(s"scala version: ${scala.util.properties.scalaproporelse("version.number", "unknown")}")     println(new dinosaur("tyrannotitan", 4900))     println(new dinosaur("animantarx ", 300))   } }  class dinosaur (name:string, weightkg: int) {   override def tostring = f"$name, weight: $weightkg kg" }  // exiting paste mode, interpreting.  defined object miniscalaapp defined class dinosaur 

only defining.so need call explicitly.

miniscalaapp.main(array()) 

in addition that, object foo extends app can't used if file have 1 top-lebel object.def mainis required.