crystal-lang/crystal

The Crystal programming language | http://crystal-lang.org | Fund Crystal's development: http://is.gd/X7PRtI | Docs: http://crystal-lang.org/docs/ | API: http://crystal-lang.org/api/

George Dietrich

@Blacksmoke16

response = HTTP::Client.get("...")
response.body # okay
response.body_io # not okay

HTTP::Client.get("...") do |response|
  response.body # not okay
  response.body_io # okay
end

From IRC (bridge bot)

@FromIRC

<SamantazFox> Why is it "not okay"?

<SamantazFox> I mean: https://gitter.im/crystal-lang/crystal?at=61a3a3c9026dc63ca61e5489

<SamantazFox> oops, wrong link

<SamantazFox> https://crystal-lang.org/api/1.2.2/HTTP/Client/Response.html#body_io%3AIO-instance-method

<SamantazFox> better

George Dietrich

@Blacksmoke16

because body_io is only set in the context of using the block overload, so body wouldnt be set

while if you used the non block overload body is set and body_io is not

by "not okay" meaning it'll raise saying it shouldn't be nil

if you try to use it in not the right context

From IRC (bridge bot)

@FromIRC

<SamantazFox> Oh, I misunderstood the code snippet you provided

<SamantazFox> Ok, I get it now.

<SamantazFox> Why isn't that mentionned in the API doc?!

George Dietrich

@Blacksmoke16

see crystal-lang/crystal#9901

From IRC (bridge bot)

@FromIRC

<SamantazFox> Ok, thanks y'all

<SamantazFox> Now, I'm wondering why it works sometimes, and not others.

<SamantazFox> And of course impàlement that properly

From IRC (bridge bot)

@FromIRC

<SamantazFox> https://play.crystal-lang.org/#/r/ccvk

<SamantazFox> What's the most recommended? Foo::Bar.echo or Toto::Foo::Bar.echo

George Dietrich

@Blacksmoke16

probably doesnt really matter, could argue the former since its shorter, or the latter because its more clear what specific type it points to

j8r

@jrei:matrix.org

[m]

In rare cases you have no choice of the latter if the stdlib uses the same name

From IRC (bridge bot)

@FromIRC

<SamantazFox> mmmh, okay, thanks :⁠)

Paulo Coghi

@paulocoghi

@naqvis Wow!

Ali Naqvi

@naqvis

:+1:

From IRC (bridge bot)

@FromIRC

<spuun> I have a MetaVar (from @type.instance_vars) which i know is a Hash, but i want to get the key and value types. How? I want to go from the MetaVar to a HashLiteral, I think?

From IRC (bridge bot)

@FromIRC

<spuun> type.type_vars is enough

George Dietrich

@Blacksmoke16

:thumbsup:

Paulo Coghi

@paulocoghi

newbie question: Is it possible to dynamically call an instance method, passing the instance variable name by string?

George Dietrich

@Blacksmoke16

not built in, but it's technically possible to re-create

there is no#send like in Ruby, but id consider redesigning it so you dont need to do that?

Max Fierke

@maxfierke

https://github.com/wyhaines/Send.cr is one such approach to dynamic dispatch in Crystal

Paulo Coghi

@paulocoghi

I am implementing this concept in Crystal (from FeathersJS framework):

A library where you can "register" services (that is, class instances) with defined "expected" methods

The main library allow the "registration" of one or more instances

The classes are created by the developer, which must have one or more methods (from the expected ones)

And the library is responsible to (automatically) expose each service on the desired protocol, like a REST API, or Socket, etc

Max Fierke

@maxfierke

one option would be to use the macro finished hook on the base class to collect all the registered sub-classes and do what you need to there

(see https://crystal-lang.org/reference/syntax_and_semantics/macros/hooks.html)

an example of this is in a program where I use the sub-classes of a base class to generate a table/hash of CLI options: https://github.com/maxfierke/mstrap/blob/d5a53cfdd809e35594ec55e58c599edffcd7c2dc/src/mstrap/step.cr#L68-L78

Paulo Coghi

@paulocoghi

Thank you @Blacksmoke16 and @maxfierke

but id consider redesigning it so you dont need to do that?

Agree

From my little knowledge, it seems that using macros is a possible solution, as Max explained with examples

George Dietrich

@Blacksmoke16

https://athenaframework.org/EventDispatcher/ may also be helpful?

define listeners on specific events, the the core logic emits those events

Paulo Coghi

@paulocoghi

Interesting! I will see if I can "automate" this process (or part of it) in order to reduce the syntax for the final developer

In simple terms, I am building a framework with an architecture based on the continuous passing style.

The experience I would like to provide is something like this (the example below is just a draft/idea, not a valid Crystal program) :

Paulo Coghi

@paulocoghi

require "Framework"

# services
require "Users"
require "Messages"

backend = Framework.new()

# create the API endpoint /users
backend.use( "users", Users.new() )

# create the API endpoint /messages
backend.use( "messages", Messages.new() )

# expose the API and listen on the default port
backend.start()

After defining the "services", the develop can "hook" functions before and after a method from a service, creating a "chain" of functions (continuous passing style here), in order to express the business rules (or contract) for each method

George Dietrich

@Blacksmoke16

hmm, how would it handles route arguments and such? I'm not familiar with this pattern, but curious to hear the benefits over other existing frameworks

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