Rails syntax error, but why?

Question

I am getting:

 syntax error, unexpected '=', expecting keyword_end diamond.send(field) = fields[field]

But I don't see why though. I am trying to dynamically assigning values.

Here is the code:

  def self.import(file)
    CSV.foreach(file.path, headers: true) do |row|

      diamond = find_by_id(row["id"]) || new

      fields = row.to_hash

      # assign non float attributes to columns
      ['cust_ref', 'ags_1st_number', 'ags_ending_number', 'gold_cut_grade', 
      'polish_grade', 'symmetry_grade', 'color_grade', 'fluor_desc', 
      'clarity_grade', 'girdle_min_max_percentage', 'diameter_min_max', 
      'girdle_condition', 'proportion_grade', 'comment_1', 'comment_2', 
      'comment_3', 'comment_4', 'is_non_ideal', 'key_to_symbols', 'shape'].each do |field|
     diamond.send(field) = fields[field]
    end
  end
end

You need to write diamond.send(field + '=', fields[field]) I think.. Because the way you are assigning is not valid. — Arup Rakshit
– Arup Rakshit, Commented Jul 1, 2014 at 18:31

the Tin Man · Accepted Answer · 2014-07-01 23:28:11Z

4

That's because you are calling the getter and not the setter.

To use send, you need to distinguish between the attr_accessor's given methods. So, for example:

class Test
   attr_accessor :field
end

t = Test.new

t.send(:field)
#=> nil
t.send(:field=, 'lalala')
#=>'lalala'
t.send(:field)
#=>'lalala'

And this works with strings too.

[EDIT] As mentioned by @jordan, this also allows you to do string interpolation, using or not symbols. So the next lines would also work:

a = 'field='
t.send(:"#{a}", 'lalala')
t.send(a)
b = 'field'
t.send("#{b}=", 'lalala')

And so on.

edited Jul 1, 2014 at 23:28

the Tin Man

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answered Jul 1, 2014 at 18:33

Afonso Tsukamoto

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9 Comments

Jordan Running Over a year ago

Important to note that if you have the name of the attribute (e.g. "field" or :field) in a variable, you can add the equals sign using ordinary string (or symbol) interpolation: t.send(:"#{attr_name}=", 'lalala').

Jordan Running Over a year ago

"#{attr_name}=" evaluates a string whereas :"#{attr_name}" evaluates to a symbol. send will take either, although IIRC in old versions of Ruby it took only symbols. In practice it doesn't make much of a difference, so it's mostly a matter of taste.

Jordan Running Over a year ago

@ArupRakshit To do interpolation in a symbol you need the quotation marks. If attr_name has a value of "foo", then :"#{attr_name}=" evaluates to the symbol :foo=. :#{attr_name}= is a syntax error.

Arup Rakshit Over a year ago

@Jordan Makes sense now.. If version of Ruby don't support #send with first argument as a string, then only :"#{attr}=" is needed to do.. otherwise not.. Perfect, got now what you meant to say..

Jordan Running Over a year ago

@AfonsoTsukamoto It's true that symbols are more memory-efficient in certain circumstances (e.g. when you have a lot of duplicate strings that are in different places in memory, although copy-on-write in Ruby 2.0 mitigates this a lot). However it's important to remember that they're never garbage-collected, and so can become a problem if, say, you have code creating lots of long symbols with different names. There was even a Rails vulnerability relating to this, because its YAML parser automatically instantiated symbols of arbitrary length. Symbols are great, but they're not a silver bullet.

|

Chubas · Accepted Answer · 2014-07-01 18:36:59Z

1

The syntax you are proposing is not a valid assignment syntax in Ruby.

You can define assignment methods in Ruby (check http://joeyates.info/2012/01/16/ruby-bareword-assignment-and-method-calls-with-implicit-self/ for a more deep-in explanation of assignment).

class Diamond
  def proportion_grade=(arg)
    @proportion_grade = arg
  end
end

If you declared an attr writer or accessor, this is done for you

class Diamond
  attr_accessor :proportion_grade
end

so what you want to call is the method proportion_grade=, not really proportion_grade

the correct way would be:

['all', 'those', 'arguments'].each do |field|
   diamond.send("#{field}=", fields[field])
end

answered Jul 1, 2014 at 18:36

Chubas

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Comments

La-comadreja · Accepted Answer · 2014-07-01 18:46:46Z

0

It seems diamond.send(field) is a method and you shouldn't treat a method call like a variable that is being declared. Declare another variable if you want to save fields[field] as a variable. Delete the "= fields[field] from the line and just put diamond.send(field) on its own line, or diamond.send(field + '=' + fields[field]) as per @Arup Rakshit.

edited Jul 1, 2014 at 18:46

answered Jul 1, 2014 at 18:31

La-comadreja

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