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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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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answer
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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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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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answers
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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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answers
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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, ...
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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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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
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votes
3
answers
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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 ...
- 296k
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votes
8
answers
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Good example of implicit parameter in Scala? [closed]
So far implicit parameters in Scala do not look good for me -- it is too close to global variables, however since Scala seems like rather strict language I start doubting in my own opinion :-).
...
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votes
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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 ...
- 1,437
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votes
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answers
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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 ...
- 10.2k
56
votes
7
answers
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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
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
52
votes
1
answer
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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
50
votes
1
answer
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views
Unexpected implicit resolution based on inference from return type
Given a typeclass where instance selection should be performed based on the return type:
case class Monoid[A](m0: A) // We only care about the zero here
implicit def s[T] : Monoid[Set[T]] = Monoid(...
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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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answers
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How to declare traits as taking implicit "constructor parameters"?
I'm designing a class hierarchy, which consists of a base class along with several traits. The base class provides default implementations of several methods, and the traits selectively override ...
- 103k
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votes
6
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?
- 1,209
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Scala: Passing one implicit parameter implicitly and the other explicitly. Is it possible?
Let's consider the function:
def foo(implicit a:Int, b:String) = println(a,b).
Now, let us assume that there is an implicit String and Int (implicit val i1=1) in scope but we want to pass an other, ...
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votes
4
answers
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Is there a way to declare an implicit val inside a for comprehension?
I have some code with nested calls to flatMap like so:
foo.flatMap(implicit f => bar(123).flatMap(b =>
/* and so on... implicit f is still in scope here.*/
))
Normally, one would write that ...
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votes
1
answer
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Log implicits only for "diverging implicit expansion"s
Other answers suggest using "-Xlog-implicits" option for debugging "diverging implicit expansion" errors. However, it also logs a lot of implicits in places unrelated to these errors. Is there some ...
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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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Conditions under which compiler will not define implicits (constructor, destructor, copy constructor, copy assignment) [duplicate]
This is supposed to be a trivial question but I could not find it explicitly on stackoverflow.
The following will be defined implicitly if not provided by the user.
default (parameterless) ...
- 4,701
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votes
3
answers
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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
2
answers
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"Cannot find an implicit ExecutionContext" error in scala.js example app.
Here is an example from the Hands-on Scala.js ebook:
package webpage
import org.scalajs.dom.ext.Ajax
import scala.scalajs.js
import scala.scalajs.js.annotation.JSExport
import scalatags.JsDom.all._
...
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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?
- 12.6k
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votes
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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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votes
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What are implicit objects?
I was reading about type classes where implicit objects were mentioned:
object Math {
trait NumberLike[T] {
def plus(x: T, y: T): T
def divide(x: T, y: Int): T
def minus(x: T, y: T): T
...
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23
votes
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answers
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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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Scala implicit object vs implicit val
I've seen two ways (one less than the other) of declaring implicit for typeclass pattern in Scala.
implicit val instance1 = new Typeclass { def do = ??? }
implicit object instance2 extends Typeclass ...
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votes
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How make implicit Ordered on java.time.LocalDate
I want to use java.time.LocalDate and java.time.LocalDateTime with an implicit Ordered like:
val date1 = java.time.LocalDate.of(2000, 1, 1)
val date2 = java.time.LocalDate.of(2010, 10, 10)
if (date1 &...
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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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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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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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Is there a systematic way to discover which implicit defs are in scope, and which one is bound at a particular point?
Often there's no need to pay any attention to implicit arguments in Scala, but sometimes it's very helpful to understand how the compiler is automatically providing them. Unfortunately, this ...
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views
How does implicit <:< help to find type parameters
A couple of questions arise while I'm reading 7.3.2 Capturing type constraints
from Joshua's Scala in Depth. The example excerpted from the book:
scala> def peek[C, A](col: C)(implicit ev: C <:&...
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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
20
votes
1
answer
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Not able to import Spark Implicits in ScalaTest
I am writing Test Cases for Spark using ScalaTest.
import org.apache.spark.sql.SparkSession
import org.scalatest.{BeforeAndAfterAll, FlatSpec}
class ClassNameSpec extends FlatSpec with ...
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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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How can I get implicit conversions to work inside collections?
Say I have an implicit conversion:
implicit def aToB(a: A):B={
...
}
How can I get this implicit conversion to work on the elements of a List?
If I have:
val listOfA: List[A] ...
and I have a ...
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Scala dependency injection: alternatives to implicit parameters
Please pardon the length of this question.
I often need to create some contextual information at one layer of my code, and consume that information elsewhere. I generally find myself using implicit ...
- 10.1k
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votes
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answers
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Xcode C++ Vectors: Implicit instantiation of undefined template
I ran this code on a different IDE and it was successful. For some reason I get the above error message on Xcode. I assume I'm missing a header of some kind, but I'm not sure which one.
#include <...
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Best way to handle false unused imports in intellij
Intellij falsely marked some import of Scala implicits as not being use.
Is there a way to prevent it from deleting those import when optimized them explicitly for a specific import and not prevent ...
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Other programming languages that support implicits "a la Scala"
Scala implicits are very powerfull. I'm curious if they are a new/unique feature of Scala, or the concept already existed in other programming languages.
Thanks.
EDIT:
To clarify my question, yes, ...
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Magnet pattern and overloaded methods
There is a significant difference in how Scala resolves implicit conversions from "Magnet Pattern" for non-overloaded and overloaded methods.
Suppose there is a trait Apply (a variation of a "Magnet ...
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Why in C# an explicit decimal => long conversion operator is called implicitly, losing precision? [duplicate]
The following C# program silently and implicitly calls an explicit decimal-to-long conversion operator, losing precision.
I don't understand why this happens. As far as I understand, in C# explicit ...
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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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Why do we still need a .lib stub file when we've got the actual .dll implementation?
i'm wondering why linkers can not do their job simply by consulting the information in the actual .dll files that got the actual implementation code ? i mean why linkers still need .lib files to do ...
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Passing scala.math.Integral as implicit parameter
I have read the answer to my question about scala.math.Integral but I do not understand what happens when Integral[T] is passed as an implicit parameter. (I think I understand the implicit parameters ...
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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 ...
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