Using an iterator to tabulate statistics

[tttwang23]

I am using an iterator to tabulate some statistics about the data it traverses over. I ran into a problem that calling map() or using a "for loop" moves the iterator, so that it is not possible to get at the saved statistics.

Are there workaround to this problem? Do I have to create this iterator passing in a mutable reference of the stat holder?

[quinedot]

If I is an iterator, then &mut I is also an iterator that just defers to I's implementation. So within a function body (for example) you can replace

for item in iterator { /* ... */ }
// Moved :-(
// let stats = iterator.stats();

with

for item in &mut iterator { /* ... */ }
let stats = iterator.stats(); // Still there :-)

And you can do something similar for the map, but you won't be able to create a map containing the &mut and return it up a call stack, say. So something more involved may be called for depending on your use case.