Rust the method map exists but how to#
Rust the method map exists but generator#

Or I could still process the file line-by-line, and use a for loop while keeping the notion of a “current” record, which I push into a vector when it is completed. I could read the whole file into a string and split it on the blank lines in order to get an array where each element is a record, and then process each record. My usual approach so far has been to split the file into lines and process each line using a chain of iterators, but maybe it’s better to let go of that approach for today. So first I think a bit about how I will process the data into records. I start out by downloading the input file and put it in the project directory, as usual. The answer to the puzzle is the number of valid passports in the input file. A record is valid if it contains all the required keys. The cid key is optional, and all the others are required. There are eight possible keys, each consisting of three letters. These records consist of whitespace-separated key:value pairs, and records are separated by blank lines. Today’s puzzle is processing records that represent “passports”. This works, and looks like what I had in mind. However, maybe I can write read_lines() so that it at least calls expect() on the io::Lines iterator that it returns: By trying things and following the compiler’s suggestions, I end up with the awkward return type of iter::Map>, dyn FnMut(io::Result) -> &String>, but this is still producing errors about lifetimes that I don’t understand. Unfortunately, I get a type that I don’t think I can put into my program! The compiler says “expected unit type (), found struct Map>, 31:46]>” I am guessing that referring to a type by the file in which it’s found and the lines and columns that it spans, is not legal Rust syntax! This article suggests asking the compiler by returning the empty type () and letting it suggest what to return instead, so I do that. I google “rust return iterator” and the first result is encouragingly titled “Returning Rust Iterators”.

Rust the method map exists but how to#

For example, io::Lines is the iterator that lines() returns, and I know it is an iterator of Results of strings, because the documentation says so, but I don’t know how to build my own iterator type. The iterator types that are returned from standard library functions all seem to be type aliases of some sort. But I cannot figure out how to write an iterator type. Where ? ought to be something like Iterator. Iterate over everything.Let file = fs::File::open(filename).expect('Bad file') contains_key( 'Les Misérables') ', book_reviews) When collections store owned values (String), they can still be // queried using references (&str). Type inference lets us omit an explicit type signature (which // would be `HashMap` in this example). If you implement these yourself, it is important that the following This can frequently be achieved by using #. It is required that the keys implement the Eq and Hash traits, although There are many alternative hashing algorithms available on crates.io. The hashing algorithm can be replaced on a per- HashMap basis using theĭefault, with_hasher, and with_capacity_and_hasher methods. Strings, though those algorithms will typically not protect against It for small keys such as integers as well as large keys such as long

While its performance is veryĬompetitive for medium sized keys, other hashing algorithms will outperform Subject to change at any point in the future. The default hashing algorithm is currently SipHash 1-3, though this is Low such as during system boot may be of a lower quality. In particular, seeds generated when the system’s entropy pool is abnormally

Rust the method map exists but generator#

Quality of the system’s random number generator when the seed is created. Because of this, the randomness of the seed depends on the output

Secure source of randomness provided by the host without blocking the Reasonable best-effort is made to generate this seed from a high quality, A hash map implemented with quadratic probing and SIMD lookup.īy default, HashMap uses a hashing algorithm selected to provide