Iterating over Results

An Iter::map operation might fail, for example:

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Let's step through strategies for handling this.

Ignore the failed items with filter_map()

filter_map calls a function and filters out the results that are None.

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Collect the failed items with map_err() and filter_map()

map_err calls a function with the error, so by adding that to the previous filter_map solution we can save them off to the side while iterating.

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Fail the entire operation with collect()

Result implements FromIterator so that a vector of results (Vec<Result<T, E>>) can be turned into a result with a vector (Result<Vec<T>, E>). Once an Result::Err is found, the iteration will terminate.

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This same technique can be used with Option.

Collect all valid values and failures with partition()

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When you look at the results, you'll note that everything is still wrapped in Result. A little more boilerplate is needed for this.

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