Hi
This following program shows many allocations coming
from boost::split(..., boost::is_any_of(",")):
```
$ cat split.cpp
#include <string>
#include <cstdio>
#include
#include
int main() {
std::string str = "foo,bar,foobar,quux";
std::size_t s = 0;
for (int i = 0; i < 100; ++i) {
boost::container::small_vector v;
#ifdef USE_IS_ANY_OF
boost::split(v, str, boost::is_any_of(","));
#else
boost::split(v, str, [](const char c) { return c == ',';});
#endif
s += v.size();
}
fprintf(stderr, "%zu\n", s);
}
```
When using boost::is_any_of(","), there are 7 dynamic allocations
per loop iteration whereas when using the lambda predicate,
there are 0 dynamic allocation per loop as shown below:
```
$ clang++ -std=c++14 -DUSE_IS_ANY_OF split.cpp
$ heaptrack ./a.out
...
allocations: 702
$ clang++ -std=c++14 split.cpp
$ heaptrack ./a.out
...
allocations: 2
```
I suspect that there are potential optimizations in Boost here to
avoid so many allocations when boost::is_any_of(",") is used.
Regards
Dominique
