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Why are "context" dependencies so often passed implicitly in Scala?


By : Dave
Date : August 02 2020, 08:00 AM
seems to work fine Deserializers are usually typeclasses, and the way that Scala implements typeclasses is via implict arguments. Doing this manually is going to be a lot more code and require the programmer to do type matching that the compiler can do itself with a typeclass.
A better example of a simple dependency would be ExecutionContext in scala.util.Future methods, and in this case it simplifies the calling code and makes it easier to provide a different context within a given scope.
code :


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What is the Scala identifier "implicitly"?


By : user2345969
Date : March 29 2020, 07:55 AM
will help you Here are a few reasons to use the delightfully simple method implicitly.
To understand/troubleshoot Implicit Views
code :
scala> 1.min(2) // Int doesn't have min defined, where did that come from?                                   
res21: Int = 1

scala> implicitly[Int => { def min(i: Int): Any }]
res22: (Int) => AnyRef{def min(i: Int): Any} = <function1>

scala> res22(1) // 
res23: AnyRef{def min(i: Int): Int} = 1

scala> .getClass
res24: java.lang.Class[_] = class scala.runtime.RichInt
scala> 1: scala.runtime.RichInt
res25: scala.runtime.RichInt = 1
scala> implicitly[Int => scala.runtime.RichInt]
res26: (Int) => scala.runtime.RichInt = <function1>
def foo[A](implicit ma: M[A])
def foo[A: M]
def foo[A: M] = {
   val ma = implicitly[M[A]]
}
trait Show[T] { def show(t: T): String }
object Show {
  implicit def IntShow: Show[Int] = new Show[Int] { def show(i: Int) = i.toString }
  implicit def StringShow: Show[String] = new Show[String] { def show(s: String) = s }

  def ShoutyStringShow: Show[String] = new Show[String] { def show(s: String) = s.toUpperCase }
}

case class Person(name: String, age: Int)
object Person {
  implicit def PersonShow(implicit si: Show[Int], ss: Show[String]): Show[Person] = new Show[Person] {
    def show(p: Person) = "Person(name=" + ss.show(p.name) + ", age=" + si.show(p.age) + ")"
  }
}

val p = Person("bob", 25)
implicitly[Show[Person]].show(p)
Person.PersonShow(si = implicitly, ss = Show.ShoutyStringShow).show(p)

Haskell: What does the warning "Variable is implicitly quantified due to a context" mean?


By : Kathrina Hilario
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You have a free type variable in your type synonym which you haven't dealt with. To take the extreme example, if we removed your a parameter, we'd have something like
code :
type SafeReturn = [e] -- Using a * -> * type instead of a * -> * -> * type
type SafeReturn a = forall e. Exception e => Either e a

"Failed to set up execution context" when running VC++ unit test with external dependencies


By : user1443902
Date : March 29 2020, 07:55 AM
around this issue So the issue here was kinda peculiar to my configuration but also generic enough to deserve an answer for other devs who might incur in this situation.
The problem was that the .dlls of my source project were not deployed to the test output folder. So you need to set OutDir in your test project properties:
code :
<PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
  <LinkIncremental>true</LinkIncremental>
  <OutDir>$(ProjectDir)$(Platform)\$(Configuration)\</OutDir>
</PropertyGroup>

Why is "this" being implicitly passed as a parameter whenever trying to invoke a constructor or a method?


By : siddharth khanna
Date : March 29 2020, 07:55 AM
wish helps you Probably the most direct way to understand why you need to implicitly pass the this reference to every non-static function you call is to show you how such a function call works 'under the hood'.
Let's take a simple example like
code :
class Test {
    public void foo(int arg) {}
    public static void bar(int arg) {}
    public void baz() {
        foo(1);
        bar(2);
    }
}
public void baz();
Code:
   0: aload_0           // Push 'this' as the first parameter onto the stack
   1: iconst_1          // Push 1 as the second parameter onto the stack
   2: invokevirtual #2  // Call 'foo'
   5: iconst_2          // Push 2 as the first parameter onto the stack
   6: invokestatic  #3  // Call 'bar'
   9: return 

Spring Boot 1.5.1 and "The dependencies of some of the beans in the application context form a cycle"


By : L.Will
Date : March 29 2020, 07:55 AM
I hope this helps you . Find out which bean(s) is the reason for cycle from logs and use @Lazy annotation with @Autowired for this bean(s) in your code. For most cases this should do the trick.
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