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Please try to avoid dependencies to third-party libraries and frameworks.

Other implementations
s := '';
for b in a do s := s + IntToHex(b,2);
s = a.unpack("H*")
s = a.hex()
import std.digest;
s = a.toHexString;
use hex::ToHex;
let mut s = String::with_capactiy(2 * a.len());
a.write_hex(&mut s).expect("Failed to write");