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Is it an issue need to be resolved? += (("a", 1))
#20066
dongxuwang
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General Discussion
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For += with tuple, why I have to add () to wrap the tuple value
import collection.mutable.ArrayBuffer val x: ArrayBuffer[(String, Int)] = ArrayBuffer(("a", 1)) // x += ("b", 2) // this wouldn't work x += (("b", 2))
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Replies: 2 comments
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Apparently, we untuple tuple arguments of infix operations if the function does not consist only of unary alternatives.
trait Buffer1[A]: def += (elem: A): Buffer1[A] val b1: Buffer1[(String, Int)] = ??? b1 += ("a", 1) // Ok trait Buffer2[A]: def += (elem: A): Buffer2[A] def += (elem1: A, elem2: A): Buffer2[A] val b2: Buffer2[(String, Int)] = ??? b2 += ("b", 2) // Error
scala3/compiler/src/dotty/tools/dotc/typer/Applications.scala
Lines 1231 to 1239 in 6bb6b43
/** Should we tuple or untuple the argument before application?
* If auto-tupling is enabled then
*
* - we tuple n-ary arguments where n > 0 if the function consists
* only of unary alternatives
* - we untuple tuple arguments of infix operations if the function
* does not consist only of unary alternatives.
*/
def needsTupledDual(funType: Type, pt: FunProto)(using Context): Boolean =
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Since the alternative Growable#+= is deprecated, it would be handy if it were ignored for purposes of infix untupling. Hopefully it can be removed someday.
The current nice syntax is x += "b" -> 2.
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