Insert format name = value in Ruby

Question

I would like to add some debugs for my simple ruby ​​functions, and I wrote a function as shown below,

def debug(&block)
  varname = block.call.to_s
  puts "#{varname} = #{eval(varname,block)}"
end

debug {:x} #prints x = 5
debug {:y} #prints y = 5

I understand that eval is evil. Therefore, I have two questions.

• Is there a way to write this debugging method without using eval? If NO is the preferred way to do this?
• Is there a way to pass a list of arguments to this method? Ideally, I would prefer debug {: x ,: y .: anynumOfvariables}. I could not understand how this would affect the debugging method (i.e., take a list of arguments).

Answer 1

Just use arrays. You can use the method Arrayto make sure you always have an array, even if someone passes only one value:

def debug(&block)
  Array(block[]).each do |var| puts "#{var} = #{eval var.to_s, block}" end
end

x, y = 3, 5

debug {:x} # => "x = 3"
debug {[:x, :y]} # => "x = 3" "y = 5"

BTW: , Ruby 1.9. ( , , .) Proc#binding, Binding Proc:

def debug(&block)
  Array(block.()).flatten.each do |var|
    puts "#{var} = #{eval var.to_s, block.binding}"
  end
end

, Ruby 1.8, , .

. , debug , . ?

def debug(*vars, bnd)
  vars.each do |var|
    puts "#{var} = #{eval var.to_s, bnd}"
  end
end

x, y = 3, 5

debug :x, binding # => "x = 3"
debug :x, :y, binding # => "x = 3" "y = 5"

, , , callsite, . .

---

: - Ruby 1.9.2 (Proc#parameters):

def debug(&block)
  block.parameters.map(&:last).each do |var|
    puts "#{var} = #{eval var.to_s, block.binding}"
  end
end

x, y = 3, 5

debug {|x|} # => "x = 3"
debug {|x, y|} # => "x = 3" "y = 5"

Answer 2

each, ?

. , .

:

def get_varname(&block)
    varname = block.call.to_s
    return varname
end

def create_instance_hash(env_attrs_obj, *attributes)
    if not env_attrs_obj.has_key?("instances")
        env_attrs_obj["instances"] = ""
    end
    attributes.each do |attr|
        attr_name = get_varname{:attr}
        env_attrs_obj["instances"][attr_name] = attr
    end
end

instance_nat_ip_pub = "ip_pub_addr"
instance_nat_ip_prv = "ip_addr"
instance_nat_ami = "AMI_NAME"
instance_nat_aws_ssh_key_id = "AWS_SSH_KEY_ID"
instance_nat_id = "instance_id"

env_hash = {}

create_instance_hash(env_hash, *[instance_nat_ip_pub, instance_nat_ip_prv, instance_nat_ami, instance_nat_aws_ssh_key_id, instance_nat_id])

:

def attrs_each_test(*attributes)
    attributes.each do |attr|
        puts get_varname{:attr}
    end
end

:

attr
attr
attr
attr
attr

create_instance_hash:

Line 12:in `[]=': string not matched (IndexError)
    from t.rb:12:in `create_instance_hash'
    from t.rb:10:in `each'
    from t.rb:10:in `create_instance_hash'
    from t.rb:24

?