Ruby: Convert String to Symbol during String Interpolation

Question

I am looping over a block of code, each time increasing variable "filter_index", from 1, to 2, to 3... etc.

I'd like to use this variable to access the different symbols:

filter1_field_name, filter2_field_name, filter3_field_name

@filter1_field_name = "Region"
@filter2_field_name = "Country"
@filter3_field_name = "City"

SELECT_STATEMENT = "GROUP BY "

numberOfFilters = 3

filter_index = 1
numberOfFilters.times do #Number of iterations 
    filter_field_name = "@filter#{filter_index.to_s}_field_name"
    SELECT_STATEMENT.sub! "GROUP BY", "AND #{filter_field_name.to_sym} GROUP BY"
  filter_index += 1
end

puts SELECT_STATEMENT

This results in

AND @filter1_field_name AND @filter2_field_name AND @filter3_field_name GROUP BY

But the desired result is

AND Region AND Country AND City GROUP BY

I'm wondering why filter_field_name.to_sym is not working (or rather, what I'm doing wrong)?

The provided answers will do what you want. However, I suggest you consider storing the filters in an array, where item 0 of the array would be the first filter, item 1 would be the 2nd filter and so on. — BrunoF
– BrunoF, Commented Jul 29, 2016 at 13:44
.to_s can be removed as interpolation (#{}) is already doing that implicitly. — cremno
– cremno, Commented Jul 29, 2016 at 13:44

thaleshcv · Accepted Answer · 2016-07-29 13:15:54Z

1

You can use instance_variable_get function to get variable value.

Replace the line

filter_field_name = "@filter#{filter_index.to_s}_field_name"

with

filter_field_name = instance_variable_get("@filter#{filter_index.to_s}_field_name")

EDIT:

I think you can put the field names into an array and concat the values with join method.

fields = ['Region','Country','City']
fields.join(' AND ')

answered Jul 29, 2016 at 13:15

thaleshcv

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2 Comments

Hendrik Kleine Over a year ago

Thanks, perfect. Learned something else!

Cary Swoveland Over a year ago

.to_s is unnecessary.

Oleh Sobchuk · Accepted Answer · 2016-07-29 13:18:15Z

0

you can use instance_variable_get or eval

filter_field_name = instance_variable_get("@filter#{filter_index.to_s}_field_name")

or

filter_field_name = eval("@filter#{filter_index.to_s}_field_name")

answered Jul 29, 2016 at 13:18

Oleh Sobchuk

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