[boost] Why protect()?

From: alex (guangzhouwangzheng_at_[hidden])
Date: 2005-05-17 23:05:53

I test the sample in the section "Nesting STL algorithm invocations":
--------------------------------------

int a[100][200];
int sum = 0;

std::for_each(a, a + 100,
              bind(ll::for_each(), _1, _1 + 200, protect(sum += _1)));
------------------------------------------------If I remove the protect
function, and I will get a complie error.Thx!