Questions tagged [callbyname]
86 questions
4
votes
1 answer
What's the type of `=> String` in scala?
In scala, there is some call-by-name parameters:
def hello(who: => String) = println("hello, " + who)
What's the type of the parameter who?
It shows the function on scala REPL as:
hello: (who: => String)Unit
Is the type still => String? Is there…
Freewind
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3
votes
2 answers
Can Scala's "call by name" be considered as a syntactic sugar of Java8's Functional Interface API?
Example of Scala's "call be name":
def giveMeName(b: => String)
Java result:
public class some.package.CallByNameEx {
public void giveMeName(scala.Function0);
public some.package.CallByNameEx();
}
Example of Java's…
6harat
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3
votes
2 answers
Non-strict by-name arguments in Python?
Question
Is there any way to declare function arguments as non-strict (passed by-name)?
If this is not possible directly: are there any helper functions or decorators that help me achieve something similar?
Concrete example
Here is a littly…
Andrey Tyukin
- 43,673
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3
votes
2 answers
Understanding Call-By-Name in Scala
I am new to scala language, therefore I will be grateful if someone could explain me this code-snippet :
object C {
def main(args: Array[String]) = {
measure("Scala"){
println("Hello Back")
}
}
def measure(x: String)(y: =>…
sasuke
- 145
- 1
- 10
3
votes
2 answers
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
}
def todo(implicit i: Int): Unit =
…
llirik
- 148
- 7
3
votes
1 answer
Overloading function with call-by-name parameter and function with by-value parameter
Why does doSmth(() => s) not compile?
Why does the rest of the code output "value"? Is there a way to call the second function(with call-by-name parameter)?
object Test {
def main (args: Array[String]){
lazy val s: String = ""
doSmth(s)
…
ilinum
- 464
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- 11
3
votes
1 answer
Using apply ("()") on function passed in by-name parameter: evaluation is not forced?
I have a function:
def nanoTime() = {
println("Getting nano time...")
System.nanoTime // returns nanoTime
}
and another function, which takes a function
def printTime(time: => Long) = { // indicates a by-name parameter
println(">>…
dublintech
- 16,815
- 29
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- 115
2
votes
1 answer
How good is Scala By-name parameters performance?
I know how scala by-name parameters work: https://tpolecat.github.io/2014/06/26/call-by-name.html
I'm using it in a very sensitive piece of code that gets run a lot.
My questions is: Is there any performance or memory drawback?
For example, I know…
user1819676
- 369
- 1
- 12
2
votes
2 answers
Performance difference between def and val
Consider the below code where I am passing a method and a function as a parameter to map()
val list1:List[Int]=List(10,20,30)
def func1(x:Int):Int={
x+10
}
list1.map(func1)
list1.map(_+10)
I have few questions about ETA…
codingsplash
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2
votes
1 answer
Call-by-value and by-name equivalence
I'm working in a Coursera course on functional programming and at some point they discuss the difference between call-by-value and call-by-name evaluation techniques. They're some point that confuses me, they say:
Both techniques reduce to the same…
user1868607
- 2,558
- 1
- 17
- 38
2
votes
1 answer
What would this print under call-by-name and call-by-value?
I have this line of code in a toy-language. The print-function takes a list of arguments and prints those.
print(a, (a := 5, a))
Would there be a difference in the output if I used call-by-value or call-by-name? If so, what would the outputs be.
It…
Borimino
- 23
- 2
2
votes
2 answers
Pass by name implementation in C
How can I calculate the value of the arithmetic expression ^2 + 3i − 1 that is dependent on the index i by using pass-by-name mechanism in C language
9
∑ i^2 + 3i − 1
=0
through a call to a sum procedure with argument(s) passed by name
Pass by name…
Kadir Erceylan
- 41
- 4
2
votes
0 answers
Scala by name versus function parameters
This is a named parameter:
def foo(bar: => Boolean): Boolean = bar
And this is a function parameter:
def foo(bar: () => Boolean): Boolean = bar()
How do the two declarations differ? Both will be evaluated lazily and each time the parameter is…
Saish
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2
votes
1 answer
Macro variant of implicit class that allows for by-name argument
For a DSL, I want to introduce a dup extension method that basically calls Vector.fill, e.g.
import scala.collection.immutable.{IndexedSeq => Vec}
implicit final class Dup[A](private val in: A) extends AnyVal {
def dup(n: Int): Vec[A] =…
0__
- 66,707
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2
votes
1 answer
Handling by-name parameters in Scala macro
I have a macro that does some analysis on nested function applications. It matches applications and retrieve the parameter types this way:
case q"$f[..$targs](..$args)(...$otherArgs)" =>
// retrieve the list of all parameter types
val…
Lionel Parreaux
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