How can I set an object attribute dynamically in Ruby e.g.
def set_property(obj, prop_name, prop_value)
#need to do something like > obj.prop_name = prop_value
#we can use eval but I'll prefer a faster/cleaner alternative:
eval "obj.#{prop_name} = #{prop_value}"
end
Use send:
def set_property(obj, prop_name, prop_value)
obj.send("#{prop_name}=",prop_value)
end
obj.send("foo=", "bar") will break unless the foo= method is already defined (by an attribute accessor or explicit method definition). All send does is invoke an existing method using the specified arguments. See: ruby-doc.org/core-1.9.3/Object.html#method-i-send
prop_name is nested key ? foo.bar
@post.comments << @comment, how to turn it dynamic? I know that ActiveModel automatically updates the independent when I set it on the dependent, but just for curiosity :)
public_send be safer?Object#instance_variable_set() is what you are looking for, and is the cleaner version of what you wanted.
Example:
your_object = Object.new
your_object.instance_variable_set(:@attribute, 'value')
your_object
# => <Object:0x007fabda110408 @attribute="value">
Ruby documentation about Object#instance_variable_set
instance_variable_set() really sets an instance variable for a variable name that is determined at run-time. In that sense, it has the same effect as in the question, but a cleaner / clearer alternative.If circumstances allow for an instance method, the following is not overly offensive:
class P00t
attr_reader :w00t
def set_property(name, value)
prop_name = "@#{name}".to_sym # you need the property name, prefixed with a '@', as a symbol
self.instance_variable_set(prop_name, value)
end
end
Usage:
p = P00t.new
p.set_property('w00t', 'jeremy')
This answer (https://stackoverflow.com/a/7466385/6094965) worked for me:
Object.send(attribute + '=', value)
attribute has to be a String. So if you are iterating trough an array of Symbols (like me), you can use to_s.
Object.send(attribute.to_s + '=', value)
