Does C#'s `foreach` Loop Variable Reuse Cause Unexpected Behavior with Lambdas?

C#

Reuse of cycle variables: a problem left over from history foreach When using Lambda expression or anonymous method, the

cycle variable reuse of C#may cause potential problems. This reuse will lead to the problem of "closure after modified", where all Lambda expressions in the cycle reference the final value of the variable, not the current value of each iteration.

foreach The emergence of this special behavior is because the circulation variable is declared outside the circulating domain, as shown in the code conversion below:

Although some people claim that the variables declare outside the cycle will not bring performance advantages, it may only be useful to access it after the cycle is over, but this method may cause serious errors due to the closure problem.

string s;
while (enumerator.MoveNext())
{
   s = enumerator.Current;
   ...
}

Unlike the for cycle, the variable scope of the for loop is inside the cycle. This inconsistency increases unnecessary error risks and makes debugging difficult.

Although this design choice may be made before the introduction of Lambda expression and anonymous methods, it has not been modified and it will still bring problems to developers. foreach

major changes in c# 5

Acknowledged this design defect, C# 5 introduced a major change to solve it. Circular variables now act logically inside the cycle body. This means that the closure will capture the new copy of the variable at each iteration, thereby eliminating the modified closure problem.

However, the for loop will remain unchanged, and the change will not be traced back to the early C#version. Therefore, developers should continue to operate carefully when using the

cycle with Lambda expression or anonymous method. foreach

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