interpolating a string to part of a ruby method

Question

I have items that can be one of several attributes like red, yellow, green (more complex than this) and they have corresponding is_red, is_yellow, is_green booleans.

I'd like to have an api function to change this value where I pass for example:

id: 12
type: red

in my function have:

item=Item.find(id)
if item.is_ + type == true
  item.is_ + type=false
end 

How would I do this?

thx in advance

Answer 1

You cannot build variable names dynamically in Ruby without using eval, which would be dirty, but functional.

You could use method_missing on a BlankSlate object to capture free text method calls and handle them as a big dirty case statement.

The most elegant solution would be a Hash, because keys can be easily composed dynamically.

Answer 2

Use send

item = Item.find(id)

if item.send(:"is_#{type}") == true
  item.send(:"is_#{type}=", false)
end