Questions tagged [implicit]
An implicit in Scala is a function applied or a parameter provided without explicitly appearing in the source code.
implicit
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questions
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Where does Scala look for implicits?
An implicit question to newcomers to Scala seems to be: where does the compiler look for implicits? I mean implicit because the question never seems to get fully formed, as if there weren't words for ...
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votes
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answers
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Implicit type conversion rules in C++ operators
I want to be better about knowing when I should cast. What are the implicit type conversion rules in C++ when adding, multiplying, etc. For example,
int + float = ?
int * float = ?
float * int = ?
...
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votes
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answer
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views
What are Scala context and view bounds?
In a simple way, what are context and view bounds and what is the difference between them?
Some easy-to-follow examples would be great too!
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votes
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answers
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Is it possible to plot implicit equations?
I would like to plot implicit equations (of the form f(x, y)=g(x, y) eg. X^y=y^x) in Matplotlib. Is this possible?
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How can I chain implicits in Scala?
The pimp-my-library pattern allows me to seemingly add a method to a class by making available an implicit conversion from that class to one that implements the method.
Scala does not allow two such ...
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votes
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answers
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TypeError: Can't convert 'int' object to str implicitly [duplicate]
I am trying to write a text game and I have run into an error in the function I am defining that lets you basically spend your skill points after you make your character. At first, the error stated ...
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votes
11
answers
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views
What are type classes in Scala useful for?
As I understand from this blog post "type classes" in Scala is just a "pattern" implemented with traits and implicit adapters.
As the blog says if I have trait A and an adapter B -> A then I can ...
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votes
1
answer
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views
In scala 2 or 3, is it possible to debug implicit resolution process in runtime?
In scala language, implicit resolution is often done in compile-time and sometimes throws obfuscating error information, one famous example of such error is when shapeless Generic throws error ...
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votes
4
answers
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views
What is the Scala identifier "implicitly"?
I have seen a function named implicitly used in Scala examples. What is it, and how is it used?
Example here:
scala> sealed trait Foo[T] { def apply(list : List[T]) : Unit }; object Foo {
| ...
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21
votes
3
answers
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Why is there an implicit type conversion from pointers to bool in C++?
Consider the class foo with two constructors defined like this:
class foo
{
public:
foo(const std::string& filename) {std::cout << "ctor 1" << std::endl;}
foo(const bool ...
user1481860
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votes
8
answers
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Why do members of a static class need to be declared as static? Why isn't it just implicit?
Obviously there can't be an instance member on a static class, since that class could never be instantiated. Why do we need to declare members as static?
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Can we define implicit conversions of enums in c#?
Is it possible to define an implicit conversion of enums in c#?
something that could achieve this?
public enum MyEnum
{
one = 1, two = 2
}
MyEnum number = MyEnum.one;
long i = number;
If not, ...
- 6,222
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votes
7
answers
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views
ReSharper and var [duplicate]
Possible Duplicate:
Why does ReSharper want to use 'var' for everything?
I have ReSharper 4.5 and have found it invaluable so far but I have a concern;
It seems to want to make every ...
- 12.2k
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votes
3
answers
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views
Implicit keyword before a parameter in anonymous function in Scala
I understand implicit parameters and implicit conversions in Scala but I saw this for the first time today: the implicit keyword in front of a parameter in an anonymous function:
Action { implicit ...
- 1,185
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votes
1
answer
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Is there a way to control which implicit conversion will be the default used?
Suppose I have this:
class String2(val x:String) {
def *(times:Int) : String = {
val builder = new StringBuilder()
for( i <- 0 until times) {
builder.append(x)
...
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17
votes
3
answers
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views
Scala: Implicit parameter resolution precedence
Suppose we have implicit parameter lookup concerning only local scopes:
trait CanFoo[A] {
def foos(x: A): String
}
object Def {
implicit object ImportIntFoo extends CanFoo[Int] {
def foos(x: ...
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votes
8
answers
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Android, How to read QR code in my application?
In my application I need to read Qr code. I searched the net and found Zing codes however lots of developers had problem with using it and it seems it is buggy!
If i assume that my customers has qr ...
- 53k
52
votes
1
answer
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views
Can't prove that singleton types are singleton types while generating type class instance
Suppose I've got a type class that proves that all the types in a Shapeless coproduct are singleton types:
import shapeless._
trait AllSingletons[A, C <: Coproduct] {
def values: List[A]
}
...
- 139k
25
votes
3
answers
5k
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Scala Functional Literals with Implicits
Forgive me if this has already been asked elsewhere. I have a Scala syntax question involving function-values and implicit parameters.
I'm comfortable using implicits with Scala's currying feature....
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19
votes
2
answers
2k
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Using context bounds "negatively" to ensure type class instance is absent from scope
tl;dr: How do I do something like the made up code below:
def notFunctor[M[_] : Not[Functor]](m: M[_]) = s"$m is not a functor"
The 'Not[Functor]', being the made up part here.
I want it to succeed ...
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votes
5
answers
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views
Why does the compiler choose bool over string for implicit typecast of L""?
Having recently introduced an overload of a method the application started to fail.
Finally tracking it down, the new method is being called where I did not expect it to be.
We had
setValue( const ...
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5
votes
1
answer
554
views
Why is this implicit ambiguity behaviour happening?
I have a typeclass Search, which has an instance Search[A] if we have a TypeClass1[A] or a TypeClass2[A] instance. With preference given to the 1 instance.
The following compiles:
trait TypeClass1[A]...
- 399
0
votes
2
answers
514
views
Type class instance for case objects defined in sealed trait
In Scala 2.13 I have a case where I define some operation for all of types extending some sealed trait EnumType. I made it working but I'd like getTypeClass function not to be dependant on concrete ...
- 3
22
votes
3
answers
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views
How does SQL Server decide format for implicit datetime conversion?
declare @str_datetime varchar(50)
set @str_datetime='30-04-2012 19:01:45' -- 30th April 2012
declare @dt_datetime datetime
select @dt_datetime=@str_datetime
This is giving following error:
Msg ...
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votes
3
answers
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views
Why does this explicit call of a Scala method allow it to be implicitly resolved?
Why does this code fail to compile, but compiles successfully when I uncomment the indicated line? (I'm using Scala 2.8 nightly). It seems that explicitly calling string2Wrapper allows it to be used ...
- 10.2k
4
votes
1
answer
322
views
How to wrap a method having implicits with another method in Scala?
I have a method with implicits:
def f(x: String)(implicit dispatcher: ExecutionContextExecutor, mat: ActorMaterializer) = ???
And I want to create a helper method like:
def g1(y: String) = f("uri1" ...
- 751
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votes
2
answers
139
views
When doing implicit resolution with type parameters, why does val placement matter?
In one file, I have:
trait JsonSchema[T] {
val propertyType: String
override def toString: String = propertyType
}
object JsonSchema {
implicit def stringSchema: JsonSchema[String] = new ...
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votes
2
answers
129
views
In scala 3, is it possible to make covariant/contravariant type constructor to honour coercive subtyping?
This is a simple example:
object CoerciveCovariance {
trait Cov[+T]
def cast[A, B](v: Cov[A])(
implicit
ev: A <:< B
) = {
v: Cov[B]
}
}
It doesn't compile:
...
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votes
5
answers
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Get companion object of class by given generic type Scala
What I am trying to do is to make a function that would take a generic class and use a static method in it (sorry for Java language, I mean method of its companion object).
trait Worker {def doSth: ...
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votes
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answers
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Implicit return values in Ruby
I am somewhat new to Ruby and although I find it to be a very intuitive language I am having some difficulty understanding how implicit return values behave.
I am working on a small program to grep ...
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votes
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views
create an ambiguous low priority implicit
Consider the default codec as offered in the io package.
implicitly[io.Codec].name //res0: String = UTF-8
It's a "low priority" implicit so it's easy to override without ambiguity.
implicit val ...
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votes
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answers
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Is a constructor a function and is it possible to call a constructor
I came across this where one of the user comment says:
A constructor cannot be called, it is not a function. It is invoked automatically when a new object is created.
My question is that is the ...
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1
answer
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views
In scala, are there any condition where implicit view won't be able to propagate to other implicit function?
Assuming that A class called 'summoner' was defined, that is capable of summoning implicit views from the scope:
case class Summoner[R]() {
def summon[T](v: T)(implicit ev: T => R): R = ev(v)...
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vote
1
answer
454
views
Implicit view not working - is my implicit def to blame?
I'm having some trouble with an implicit view. I suspect this is quite trivial and may have some embarassingly easy answer. I have a situation like this, along with (obviously, unsuccessful) attempts ...
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1
answer
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views
In scala 2.13, how to use implicitly[value singleton type]?
The following simple code:
implicit val a: String = "abc"
implicitly[a.type]
fails to compile despite that a is totally in the scope and consistent in type:
Error:(9, 13) could not ...
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0
votes
1
answer
630
views
Pass implicit parameter through multiple objects
I wonder is it possible to pass implicit params through singletons like that
case class Greet(g: String)
object Foo {
def greet(name: String)(implicit greet: Greet = Greet("Hello")) = ...
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votes
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answers
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explicit and implicit c#
I'm new to C# and learning new words. I find it difficult to understand what's the meaning of these two words when it comes to programming c#.
I looked in the dictionary for the meaning and here's ...
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popen implicitly declared even though #include <stdio.h> is added
This is tiny snippet of my code.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include <sys/stat.h>
#include <sys/...
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"can't existentially abstract over parameterized type..."
I was messing around with Scala 2.8 for fun and trying to define a pimp which adds an "as" method to type constructors, allowing to convert from one functor to another (please overlook the fact that I'...
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How can implicits with multiple inputs be used in Scala?
For example, how can I write an expression where the following is implicitly applied:
implicit def intsToString(x: Int, y: Int) = "test"
val s: String = ... //?
Thanks
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Scala: generic weighted average function
I want to implement a generic weighted average function which relaxes the requirement on the values and the weights being of the same type. ie, I want to support sequences of say: (value:Float,weight:...
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votes
0
answers
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What are the hidden rules regarding the type inference in resolution of implicit conversions?
I thought that if the following compiles:
implicitly[X => Y]
than so will this:
(??? :X) :Y
It turns out I was wrong. Backstory: I toyed with an implementation of type unions:
private[this] val ...
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votes
1
answer
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views
Finding the second matching implicit
Consider the following setup:
trait Foo[A]
object Foo extends Priority2
trait Priority0 {
implicit def foo1: Foo[Int] = new Foo[Int] {}
}
trait Priority1 extends Priority0 {
implicit def foo2: ...
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2
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1
answer
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Scala Kleisli throws an error in IntelliJ
trying to implement Kleisli category for a made-up Partial type in Scala (reading Bartosz Milewski's "category theory for programmers", that's exersize for chapter 4)
object Kleisli {
type ...
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Shapeless3 and annotations
This is a followup on Shapeless and annotations. The original question was asked in the context of Scala 2 and Shapeless2.
Some features from Shapeless2 were migrated to Shapeless3, such as ...
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Why can't Scala find my typeclass instance defined implicitly in the companion object, when the typeclass is not in a dedicated source file?
Please refer to the source code below. All source code is defined in the same package. When I define all of the code within a single source file ShowMain.scala, I get a compile error, however when ...
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1
answer
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views
NullPointerException on implicit resolution
This code results in NullPointerException:
import anotherpackage.MyContext
import anotherpackage.builders.aMyContext
case class Context(id: String)
object Context {
implicit def `ContextHolder to ...
1
vote
1
answer
6k
views
Implicit wait Command Not Working-selenium webdriver C#
Guys, I have started to work on selenium web driver. You can assume I am a beginner. At the moment I am having difficulties in implementing the implicit wait command in my code (C#). it is not working ...
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1
answer
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What is a diverging implicit expansion error?
While trying to find a solution to another question ([1]) I came across a diverging implicit expansion error. I'm looking for an explanation about what this means
Here's the use case:
scala> ...
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Scala implicit usage choices
I've been wondering whether transparent implicit conversions are really such a good idea and whether it might actually be better to use implicits more, um, explicitly. For example, suppose I have a ...
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