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React : how to update states which have both mutable and immutable values


React : how to update states which have both mutable and immutable values

By : Yuri Dmitriev
Date : October 17 2020, 01:08 AM
wish helps you As long as you supply a new value for errorMessages, React will update the state correctly. You're not mutating state directly here, you're just providing a new value for the field, and React will do the necessary mutation:
code :
this.setState({
   errorMessages: error.response.data
   success: false,
   error: true,
});


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Scala - Update mutable maps inside immutable Vector

Scala - Update mutable maps inside immutable Vector


By : hung
Date : March 29 2020, 07:55 AM
I wish did fix the issue. The type Map is defined in Predef as scala.collection.immutable.Map.
If you want a vector with mutable maps, then you have to declare the type explicitly as collection.mutable.Map, and then you have to update the map, not the vector:
code :
import scala.collection.mutable.{Map => MutMap}

def calculate_objectives(pop: Vector[MutMap[String, Any]]): Unit = {
  for (i <- 0 until pop.size){
    pop(i)("weights") = decode(pop(i)("genome").asInstanceOf[Vector[Int]])
    pop(i)("objective") = Vector(
      objective1(pop(i)("weights").asInstanceOf[Vector[Float]]), 
      objective2(pop(i)("weights").asInstanceOf[Vector[Float]])
    )
  }
}
Mutable fields of immutable values in Scala

Mutable fields of immutable values in Scala


By : user2602063
Date : March 29 2020, 07:55 AM
will be helpful for those in need Consider a simple class and a (immutable) value instance of it: , x.m is mutable.
The following code is valid:
code :
class MyClass (var m: Int) {}

val x : MyClass = new MyClass(3)

println(x.m)

x.m = 7
println(x.m)
React State remains immutable for states represented with lists

React State remains immutable for states represented with lists


By : user3673481
Date : March 29 2020, 07:55 AM
may help you . I have a state represented by two arrangements. I must, at certain events, update one of them. The status update function is actually executed, but the status does not change, it remains with the same values before it is invoked. The status update does occur when I refresh the page, but not when the events that invoke the SetState occur. , You assigned wrong variable. Your state has
code :
{listaSensor, listaNivel, sum}
      {
        list,
        listaSensor,
        sum
      }
How to update nested states in React, should state be immutable?

How to update nested states in React, should state be immutable?


By : Sambeleleny Chicupo
Date : March 29 2020, 07:55 AM
To fix this issue You state that:
"Object.assign, this still mutate the state since newStudents is just a new reference to the same object this.state points to"
How to add values to a mutable list to then add to an immutable one

How to add values to a mutable list to then add to an immutable one


By : Yurii Kolodovskyi
Date : March 29 2020, 07:55 AM
hop of those help? You can't really "add to an immutable [list]".
If you are already using a mutable list somewhere, then you can use toList() (like in @anber's answer) to get a read-only version or you could also directly pass it to a function expecting a List (if you don't change the list while the framework is using it).
code :
val list = (1..100).map { "$it" }
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