crystal-lang

问题 In Ruby: require 'open-uri' download = open('http://example.com/download.pdf') IO.copy_stream(download, '~/my_file.pdf') How to do the same in Crystal? 回答1: We can do the following: require "http/client" HTTP::Client.get("http://example.org") do |response| File.write("example.com.html", response.body_io) end This writes just the response without any HTTP headers to the file. File.write is also smart enough to not download the entire file into memory first, but to write to the file as it reads

问题 I'm following the current crystal installation docs, my installation stops at the first moment and give the error: gpg: connecting dirmngr at '/tmp/apt-key-gpghome.4GKHZljOFL/S.dirmngr' failed: IPC connect call failed gpg: keyserver receive failed: No dirmngr I've already installed dirmngr. 回答1: First of all, you need to remove crystal.list from sources directory to install from start manually. sudo rm /etc/apt/sources.list.d/crystal.list And then: curl -s "https://keyserver.ubuntu.com/pks

问题 In Ruby, to construct a method's name and send it to an object, one can do: class Foo def foo "FOO" end end Foo.new.public_send(:foo) # => "FOO" Foo.new.public_send("foo") # => "FOO" What is equivalent technique for Crystal? 回答1: You should remember that Crystal, unlike Ruby, is a compiled, statically-typed language, so dynamic features of Ruby don't map that well to it. Crystal's alternative to dynamism is support for macros - but they are not the same, and you shouldn't expect them to work

问题 Is there a standard way to achieve the same result as in Ruby with Array#pack method: [1,2].pack­ "LL" => "\x01\x00\x00\x00\x02\x00\x00\x00" 回答1: Not yet, and most likely, it wont be. The reason is that usually the result of pack is used to be sent to an IO (do you have any other case in mind?), so instead of allocating the result in memory, we're thinking about providing equivalent methods in the IO itself to send the data directly to the socket, file, etc... It's not written in stone and

问题 Is possible to use method proc with parameters in Crystal ? Something like: def foo(baz) puts "#{baz} foo!" end proc = ->foo proc.call "Hi" 回答1: Yes. If the method has arguments, you must specify their types: proc = ->foo(String) proc.call "Hi" # Hi foo! Find more examples at crystal docs. 来源： https://stackoverflow.com/questions/46728581/method-proc-with-parameters

问题 Suppose I have an abstract struct that needs to operate on two kinds of inputs like so (for more context, see previous SO question). abstract struct Numberlike alias Num = (Int32 | Float64) abstract def - abstract def -(other : self) abstract def -(other : Num) end If my implementation can use self and Num interchangeably, it seems reasonable to just put them together: struct Term < Numberlike alias Num = (Int32 | Float64) getter coeff : Num getter sym : Symbol def initialize(@coeff, @sym);

问题 If I created processes with Process.new , they can be killed with .kill . However, they become zombies in a Signal trap: PROCESSES = {} of Int32 => Process spawn { loop { sleep 1 } } spawn { x = Process.new("sleep", "100".split) x.kill sleep 0.4 puts x.terminated? x = Process.new("sleep", "100".split) PROCESSES[x.pid] = x } Signal::INT.trap { Signal::INT.reset PROCESSES.each { |pid, x| puts "killing: #{pid}" x.kill sleep 1 puts "killed #{pid}? #{x.terminated?}" } } sleep Running this code

问题 How can I read a single char from the console without pressing enter / return? In ruby I would just use: require 'io/console' input = STDIN.getch 回答1: Try this: char = STDIN.raw &.read_char p char 来源： https://stackoverflow.com/questions/39964008/read-a-single-char-from-stdin-without-pressing-enter

问题 I have a JSON response which is an Array of Hash: [{"project" => {"id" => 1, "name" => "Internal"}, {"project" => {"id" => 2, "name" => "External"}}] My code looks like this: client = HTTP::Client.new(url, ssl: true) response = client.get("/projects", ssl: true) projects = JSON.parse(response.body) as Array This gives me an Array but it seems I need to typecast the elements to actually use them otherwise I get undefined method '[]' for Nil (compile-time type is (Nil | String | Int64 | Float64

问题 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 #