Questions tagged [implicit]
An implicit in Scala is a function applied or a parameter provided without explicitly appearing in the source code.
implicit
322
questions with no upvoted or accepted answers
53
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0
answers
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views
Materialize the Value for a Type that has One Inhabitant
Thanks to @MilesSabin's answer I can write a type level Fibonacci sequence:
sealed trait Digit
case object Zero extends Digit
case object One extends Digit
sealed trait Dense { type N <: Dense }
...
- 1,741
7
votes
0
answers
187
views
Generic method overloading via implicit class
When I try to create an extension for the class via implicit class and overload existing generic method, it fails with compilation error:
error: overloaded method value getAs with alternatives:
(...
- 2,363
6
votes
0
answers
157
views
Implicit conversion is not applied if a method has type parameter
The question is based on the discussion here. This is the setup:
implicit def CToC2(obj: C1): C2 = {
new C2()
}
class C1() {
def f[U](f: (Int, Int) => U): U = f(1, 1)
}
class C2() {
def f[...
- 5,170
6
votes
0
answers
398
views
diverging implicit expansion
Can someone please explain to me why I get a 'diverging implicit expansion error' here? I think it has to do with the type synonym type MyIdType = String but I am not sure why.
import org.scalacheck....
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6
votes
0
answers
489
views
Ambiguity in Low priority implicits
I have the following snippet of Scala code:
import java.io.PrintWriter
trait Write[-A] {
def apply(out: PrintWriter)(x: A): Unit
}
trait LowPriorityWrites {
implicit object any ...
- 33.1k
5
votes
0
answers
688
views
How to pass data model via implicit deeplink, between fragments
I need to pass a data model from one fragment to another via implicit deeplink, but I didn't find a way how to do it. I only found smth like this:
val request = NavDeepLinkRequest.Builder
.fromUri(...
- 63
5
votes
0
answers
107
views
Type Class: Not using `asInstanceOf`, but still getting `ClassCastException`
Consider the following relatively simple code:
import scala.deriving.Mirror
trait TC[A]:
def show: A
object TC:
inline def derived[A](using m: Mirror.ProductOf[A]): TC[A] = new TC[A]:
...
- 1,554
5
votes
0
answers
355
views
Why is Try the default implicit Applicative instance in cats
Playing around with cats, I have noticed a certain behavior which I cannot quite explain:
import cats.implicits._
...
def wrapA[A, F[_]](v: A)(implicit F: Applicative[F]): F[A] = F.pure(v)
not a ...
- 61k
5
votes
0
answers
210
views
How can I chain generic implicits in Scala?
There is this post that discusses chaining of implicits but I think it doesn't cover my case because I have generic implicits. Sample project that demonstrates the issue is located here. To reproduce ...
- 29.7k
5
votes
1
answer
158
views
Finding implicit values in the companion object of a nested type
I have a trait Outer with a member F that is a type constructor. I want to supply type-class instances for F, but somehow at one point the implicit resolution of scalac stops working.
I tried to ...
- 28.5k
5
votes
0
answers
538
views
Scala implicit class to Java static method for interop?
Is it possible to automatically generate companion Java static methods for interop from an implicit class definition ?
e.g.:
class Foo()
object FooOps {
implicit class FooOps(foo: Foo) extends ...
- 1,284
4
votes
0
answers
142
views
What causes AbstractMethodError for scala implicit val?
I have a gears library, depending on
"org.typelevel" %% "cats-core" % "2.7.0",
"org.typelevel" %% "cats-effect" %...
- 15.6k
4
votes
0
answers
145
views
Where should I put typeclass instances?
Lets say I develop a new public data structure, lets call it FancyList. It has no external dependencies and everybody loves it.
This FancyList turns out to be a Functor, Monad, MonoidK, and Traverse.
...
- 897
4
votes
0
answers
240
views
Scala how to create implicit object with same name as function
Given the following trait and companion object definitions:
trait Api {
def foo(s: String): String
}
object Api extends Api {
override def foo(s: String) = s
}
I would like to extend the ...
- 41.4k
4
votes
0
answers
280
views
how would one define a scala implicit in a java library?
As a bit of background, I'm using joda DateTime from Scala. It seems that everywhere a Scala developer uses Joda DateTime, they define some implicit datetimeOrdering, which they then import. Each ...
- 4,224
4
votes
1
answer
1k
views
Custom Implicit Intent in Android not working
I am testing implicit intent. I have two Small Test Applications:
1st AndroidManifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/...
- 485
4
votes
0
answers
535
views
cloth sim with implicit integration unstable problem
Im implementing a gpu based cloth simulation using mass-spring model with a backward euler integration.
The linear system is solved by using the conjugate gradient solver with filter. Everything is ...
- 41
3
votes
0
answers
43
views
Can I introduce an implicit precedence relation between packages as with objects?
I was wondering how to place effectively the same implicit conversion in more than one package in such a way that importing the contents of one is enough, but importing all doesn't introduce conflicts....
- 2,210
3
votes
0
answers
137
views
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 ...
- 2,210
3
votes
1
answer
167
views
Scala - Overloading method in implicit class
I currently have an issue where I am trying to overload a method contained within quill using an implicit class, normally this is possible with the simple case, i.e. if you have something like
class ...
- 1,889
3
votes
1
answer
178
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: ...
- 32.1k
3
votes
0
answers
3k
views
Scala implicit parameter not found
I am trying to write this object:
object Timed {
def apply[T](fn: => T)(implicit logger: Logger): T =
measureDuration(Thread.currentThread().getStackTrace.last.getMethodName, TimeUnit....
- 4,381
3
votes
0
answers
314
views
shapeless calling value on lazy make a StackOverflowError
While learning shapeless via this useful guide
I was trying to merge what I have learned from this in this exercice
The result is this code :
import shapeless._
object GenericV3 {
trait ...
- 1,645
3
votes
0
answers
305
views
How do I overload TYPE* conversion from another pointer?
I can't seem to find anything that deals with this type of operation.
I have a class TextButton : public TextDecorator class that I want to overload the implicit conversion operator for. The ...
- 598
3
votes
0
answers
249
views
Chain implicit conversion of collection
I fail make an implicit conversion List[A] => List[B], given implicit conversion A => B.
There is a very related question that has a solution but does not work for me. Also, here is a nice ...
- 1,668
3
votes
1
answer
1k
views
Implicit parameters not found
I'm having some trouble figuring out why compiler complains about not finding an implicit parameter for reads because I'm almost sure that it is in the scope. The error is the following:
Error:(13, ...
- 2,846
3
votes
2
answers
772
views
Tunnel implicit parameter to call-by-name function body
Consider following code snippet:
object Example {
def run(f: => Unit): Unit = {
implicit val i = 1
f
}
def caller(): Unit =
run {
todo
}
...
- 148
3
votes
1
answer
211
views
Implicit search does not guide type inference to find a supertype in Scala
I the following code, I have evidence of R[A] and B is a subtype of A, so I would expect foo to infer the type of A and use the RA evidence. However, scalac refuses to do so.
trait R[T]
case class A(...
3
votes
3
answers
2k
views
How to implicitly inject a value from an outer scope into a Scala trait
I'm trying to define a reusable trait that expects a value to be in an outer scope. I can define the trait inside the outer scope and it will work, but won't be reusable. When I move the trait to a ...
- 7,529
3
votes
3
answers
181
views
Transform (A => (M[B], M[C])) into (A => M[(B, C)])
I don't know the technical terminology for this, but as stated in the title, I'm looking for a function or feature of a typeclass that transforms a function outputting a pair of containers into a ...
- 1,578
3
votes
1
answer
218
views
How to detect implicit commit in MySQL?
I would like to know is it possible to detect broken transactions caused by implicit commit or no.
Currently I don't know how to check if transactions in my application works without implicit commit. ...
- 31
3
votes
1
answer
1k
views
How to register my navigation app for implicit navigation intents?
I want my navigation-app to be called via implicit intents from other apps. So I guess I need to "register" my app for such navigation-intents in its Manifest. But how exactly can I "register" as a ...
- 874
2
votes
0
answers
34
views
Extensions methods using implicits do not compile with Scala 3
Following code compiles fine with Scala 2.13.12, but not with Scala 3.3.1:
import scala.language.implicitConversions
object Types {
trait Vector3f
implicit class Vector3fOps(v: Vector3f) {
...
- 33.9k
2
votes
0
answers
50
views
Scala 3 given/implicit resolution doesn't work as expected
I'm working on the Chapter 11 Case Study: CRDTs from the excellent book "Scala with Cats". The code in the book is written using Scala 2, but I've modified it for Scala 3, specifically 3.3.1....
- 23.1k
2
votes
2
answers
2k
views
Playwright clicks element (drop down) before it is ready resulting in the drop down not opening
I have a product page containing a product with quantity options. There is a drop down to select the quantities. I want to click this to open it and select an option. The steps are simple:
Load page
...
- 31
2
votes
0
answers
132
views
Scala3 implicit conversion not working with opaque types (not true)
EDIT 2 - BEGIN: What I have not verified, and I should have, was if the conversion of my example works for regular types. And it doesn’t neither. So, the title and all my post is surely wrong.
Sorry ...
- 1,054
2
votes
0
answers
864
views
implicit instantiation of undefined template 'std::function::__1::void(int,int)
#include <QApplication>
#include <unordered_map>
#include <memory>
#include <QDebug>
#include <functional>
template<typename T,typename ...args>
class TestClassA
{
...
- 21
2
votes
1
answer
89
views
The opposite of compiletime.constValue[T] in Scala 3
If we have a transparent inline def f(...): Boolean = ..., is it possible to convert the result of f to true or false types, assuming the result of f is known at compile-time? I would like to use ...
- 1,554
2
votes
0
answers
333
views
Does using Scala implicit classes feature on Spark Dataframe is a monkey patching?
I'm trying to add side-effect functionality to Spark DataFrame by expanding DataFrame class using Scala implicit classes feature for the reason that "Dataset Transform Method" only allows ...
- 322
2
votes
1
answer
112
views
Is it possible to have a sub-trait inheirit a class parameter from another trait?
I am trying to DRY up my code a little bit. I am using Circe to do some decoding. I have several classes and all of them have the form of:
import io.circe.derivation.deriveDecoder
import io.circe....
- 588
2
votes
0
answers
224
views
Scala 3 type class fails: given_... is already defined in scope as class
If I try to compile the following code in Scala 3, I get a given_Finder_Needle_*: is already defined as class given_Finder_Needle_*
Am I doing something wrong? Is this the right way of implementing ...
- 151
2
votes
0
answers
58
views
In scala, what can be done to prevent compiler from cyclic summoning of implicit premises? And how to avoid them
I'm writing an implementation for Curry-Howard isomorphism in scala, a family of proofs can be defined as an object implementing the following trait:
(the full code repo is uploaded to https://github....
- 3,898
2
votes
1
answer
116
views
How to implement usage site variance in implicits?
Large redaction of the original question: now I present the whole code upfront, without showing the variants explaining my motivation. Apologies for the confusion.
I need a simple type class ...
- 2,210
2
votes
2
answers
674
views
sbt could not find implicit value for parameter valName
I'm using sbt to build some of the riscv boom from the source code, but the sbt complains that it "could not find implicit value for parameter valName: : freechips.rocketchip.diplomacy.ValName". The ...
- 21
2
votes
0
answers
2k
views
Why does pureconfig not find my implicit readers?
I use double to encode boolean value in a configuration file. PureConfig does not find a way to cast it while reading the configuration.
Initial question (see below for edit).
Here is some code to ...
- 3,019
2
votes
1
answer
2k
views
How to fit data to non-ideal diode equation (implicit non-linear function) and retrieve parameters
Plot of scattered data
I need to fit (x,y)-data to an equation with two variables (the x's and the y's) and retrieve the 5 unknown parameters.
I am making a script to treat IV-data (current-voltage) ...
- 21
2
votes
0
answers
1k
views
Why we need explicit exception chaining in Python 3
I have just learned about exception chaining in Python. What I see is, that there are two ways - inplicit and explicit. If I don't do anything special and raise caught exception. Py will automatically ...
- 21
2
votes
1
answer
261
views
How to solve non linear system of array using scipy
I wrote a class with the aims to solve the system of differential equations (given in numpy.array form) , in order to solve the non linear system I'm using the scipy.optimize.fsolve using an example ...
- 1,020
2
votes
0
answers
99
views
Why does extracting and assigning individual tuple values cause a recursive implicit search?
Here's the code to produce this error:
build.sbt
scalaVersion := "2.11.7"
libraryDependencies ++= Seq(
"ai.x" %% "safe" % "0.1.0"
)
scalacOptions := Seq("-Ytyper-debug") // Only add this if you ...
- 2,791
2
votes
1
answer
3k
views
Java FTP over TLS/SSL (FTPS- Implicit) Server in Java - Several Error
I am trying to connecting a server with FTPSClient (true implicit), port 990, and it seems the connection is ok, but it says that the file PDF inside cannot be found.
String protocol = "TLS"; // ...
- 79