I am reading a source code and it contains the following lines.

```
auto updateSlack = [&](const char slack_type, const double s) {
    if (slack_type == 'e') {
        wns.early_slack = min(s, wns.early_slack);
        tns.early_slack += s;
    }
    else if (slack_type == 'l') {
        wns.late_slack = min(s, wns.late_slack);
        tns.late_slack += s;
    }
};

```

I am confused with the "[&]" symbol after "=" operator. Can anyone tell what exactly this suggests?