Why weren't C# 5.0's captured closure improvements applied to `for` loops?

C# 5.0: Why for loops missed the captured closure enhancement

C# 5.0 addressed the captured loop variable problem in foreach loops, ensuring closure variables accurately reflect the loop variable's value at capture time. However, this improvement wasn't applied to for loops, which retain their pre-5.0 behavior.

The Reason for Omission

This intentional exclusion stems from fundamental differences between for and foreach loops:

• for loops: Initialization-centric. A for loop starts with an initializer assigning a value to the loop variable. This variable is central to the loop's logic, modified and checked repeatedly.
• foreach loops: Iterator-based. foreach loops rely on an iterator providing values for each iteration. The loop variable acts as a placeholder, accessing the iterator's value.

In for loops, the concept of a single "loop variable instantiation" aligns with their initialization-focused nature. There's a single, logically consistent loop variable instance, initialized, updated, and controlling loop termination.

Consider this for loop:

<code class="language-csharp">for (int i = 0; i < 10; i++) { ... }</code>

Here, i manages iteration count. It's initialized to 0, incremented each iteration, and controls loop termination. A closure capturing i would intuitively reference a single value, regardless of i's in-loop changes. This contradicts the for loop's reliance on the variable's changing state.

Conversely, foreach loops don't depend on the loop variable's state. They iterate over a collection without needing a specific variable instance. Thus, the closure captures the iterator's value at capture time, isolated from subsequent modifications.

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