scala - trait implementation -

if have traits like:

trait {...} trait b extends a{...} trait c1 extends b{...} trait c2 extends a{...} 

i can write class in 2 ways (c1 , c2 add same functionality)

class concrete1 extends b c1 class concrete2 extends b c2 

what variant better(efficient)?

they identical in terms of performance. if write test this:

object traits {   trait { def = "apple" }   trait b extends { def b = "blueberry" }   trait c1 extends b { def c = "cherry" }   trait c2 extends { def c = "chard" }   class dessert extends b c1 { }   class salad extends b c2 { } } 

and @ bytecode dessert , salad see

public traits$dessert();   code:    0:   aload_0    1:   invokespecial   #29; //method java/lang/object."<init>":()v    4:   aload_0    5:   invokestatic    #33; //method traits$a$class.$init$:(ltraits$a;)v    8:   aload_0    9:   invokestatic    #36; //method traits$b$class.$init$:(ltraits$b;)v    12:  aload_0    13:  invokestatic    #39; //method traits$c1$class.$init$:(ltraits$c1;)v    16:  return  public traits$salad();   code:    0:   aload_0    1:   invokespecial   #29; //method java/lang/object."<init>":()v    4:   aload_0    5:   invokestatic    #33; //method traits$a$class.$init$:(ltraits$a;)v    8:   aload_0    9:   invokestatic    #36; //method traits$b$class.$init$:(ltraits$b;)v    12:  aload_0    13:  invokestatic    #39; //method traits$c2$class.$init$:(ltraits$c2;)v    16:  return 

if go , @ initializers c1 , c2, they're both empty. if @ method call c, again, it's reference 1 defined either in c1 or c2.

this happens because of way layered traits interpreted. can think of them stack: each time add "with", whole inheritance hierarchy pushed onto stack except there not added again. doesn't matter whether c2 has b or not, since class salad picked b because extends b.