PHP生成器脚本累加逻辑疑问：为何输出不符合预期步长结果？

Hey Tom, let's walk through exactly what's happening in this generator function to clear up why you're seeing 6 instead of 4 as the second output!

First, let's recap the key part of your code that's driving the output:

function addieren($start, $ende, $schritt = 1) {
    if ($start < $ende) {
        $erg = 0;
        for ($i = $start; $i <= $ende; $i += $schritt) {
            $erg += $i; // This line is the critical piece
            yield $erg;
        }
    }
}

The confusion comes from what yield is returning here—it's not the current value of $i, but the running total stored in $erg. Let's break down each iteration of the loop when you call addieren(2, 10, 2):

• First iteration:

  • $i starts at 2
  • $erg (initially 0) becomes 0 + 2 = 2
  • Yield 2 → this is your first output

• Second iteration:

  • $i increments by 2 to 4
  • $erg (now 2) becomes 2 + 4 = 6
  • Yield 6 → this is why you see 6 instead of 4

• Third iteration:

  • $i increments to 6
  • $erg becomes 6 + 6 = 12 → yield 12

• Fourth iteration:

  • $i increments to 8
  • $erg becomes 12 + 8 = 20 → yield 20

• Fifth iteration:

  • $i increments to 10
  • $erg becomes 20 + 10 = 30 → yield 30

If you were expecting the output to be 2, 4, 6, 8, 10 (just each step value), you'd want to yield $i directly instead of the running total:

function addieren($start, $ende, $schritt = 1) {
    if ($start < $ende) {
        for ($i = $start; $i <= $ende; $i += $schritt) {
            yield $i; // Yield the current step value instead of the sum
        }
    }
}

That makes sense now, right? The original code is designed to return cumulative sums, not individual step values.

内容的提问来源于stack exchange，提问作者Tom