crystal-lang

Suppose a function defined like this: def composition(text : String, k : Int32) : Array(String) kmers = Array(String).new (0 .. text.size - k).each do |i| kmers << text[i, k] yield text[i, k] end return kmers end How do I check if the block argument is given inside the function? If the block argument is given, kmers will be yielded. If not given, kmers will be returned as an array of strings. Such a check is impossible, because a method accepting a block (using yield anywhere) simply has a different signature. But that also means that you don't need the check, just make 2 methods like this: #

If a Crystal language process is running as root, can it change it's euid/uid to something else? For example: old_euid, old_ui = Process.euid, Process.uid Process.euid = someone_else Process.uid = someone_else Yes, by using bindings to libc: lib LibC fun setuid(uid_t : Int) fun getuid : Int end LibC.getuid #=> 0 Process.run("whoami", output: true) #=> root LibC.setuid(uid) LibC.getuid #=> my uid Process.run("whoami", output: true) #=> my user name The program needs to be running as root of course (i. e. sudo crystal source.cr ) 来源： https://stackoverflow.com/questions/47557469/is-it-possible

I am trying to process the following JSON that I receive from an API. {"product":"midprice", "prices":[ ["APPLE","217.88"], ["GOOGLE","1156.05"], ["FACEBOOK","160.58"] ]} I can get a basic mapping working with: require "json" message = "{\"product\":\"midprice\",\"prices\":[[\"APPLE\",\"217.88\"],[\"GOOGLE\",\"1156.05\"],[\"FACEBOOK\",\"160.58\"]]}" class Midprice JSON.mapping( product: String, prices: Array(Array(String)), ) end midprice = Midprice.from_json(message) p midprice.product # Outputs the String p midprice.prices # Outputs Crystal 0.26.1 Code: https://play.crystal-lang.org/#/r/515o

Like many others, I always hold true that "A pure compiler will never exist for Ruby because the language is far too dynamic for a static compiler to work." But I recently stumbled upon these: The Crystal programming language at GitHub Statically compiled Ruby Both projects seem to be very interesting. They could give us the speed of a native-compiled language (and the often commercially-required, obfuscated code of a compiled language) while keeping all (or most) of the elegance and flexibility of Ruby. Add a good support library (or, more likely, the possibility to access the existing C++