Implicitly captured closures or Access to modified closure
It is a type of alert that Resharper shows in the code below, I would like to better understand this type of alert and what kind of problem it may cause in the code in which it is shown.
See this code to better understand:
using static System.Console;
using System;
using System.Collections.Generic;
public class Program {
public static void Main() {
var lista = new List<Action>();
for (var i = 0; i < 10; i++) {
lista.Add(() => WriteLine(i));
}
for (var c = 0; c < 10; c++) {
Metodo(lista[c]);
}
}
public static void Metodo(Action func) {
func();
}
}
See working at dotNetFiddle and CodingGround .
Before you see it running, what do you expect to happen? Who prints the numbers from 0 to 1? That's what you're warning. You probably expect something that will not happen. This code will print 10 times the number 10 which is the last value of i , the variable captured in lambda . It may be that's what you want, but it's unlikely.
The solution is to create an intermediate variable just to support lambda and capture takes place correctly. So:
var lista2 = new List<Action>();
for (var i = 0; i < 10; i++) {
var tmp = i;
lista2.Add(() => WriteLine(tmp));
}
for (var c = 0; c < 10; c++) {
Metodo(lista2[c]);
}
The error messages are:
Closures implicitly captured
This problem is related to the fact that a reference was captured by the anonymous function and will survive more than it should and it is good that you know well what it is doing, this can cause a memory leak
Access to a modified closure
Used a captured variable that does not have the value likely to be