A minimal POC to validate an IoC container in Crystal

what.cr

abstract struct Any; end
record A(T) < Any, this : T

class What
    def hello()
        puts "Hello!"
    end
end

container = {} of String => Any

container["test"] = A.new(What.new)

container["test"].this.hello

Taken from crystal-lang/crystal#4572 (comment)