Plus equals with ruby send message

Question

I'm getting familiar with ruby send method, but for some reason, I can't do something like this

a = 4
a.send(:+=, 1)

For some reason this doesn't work. Then I tried something like

a.send(:=, a.send(:+, 1))

But this doesn't work too. What is the proper way to fire plus equals through 'send'?

Answer 1

I think the basic option is only:

a = a.send(:+, 1)

That is because send is for messages to objects. Assignment modifies a variable, not an object.

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It is possible to assign direct to variables with some meta-programming, but the code is convoluted, so far the best I can find is:

a = 1
var_name = :a
eval "#{var_name} = #{var_name}.send(:+, 1)"
puts a  # 2

Or using instance variables:

@a = 2
var_name = :@a
instance_variable_set( var_name, instance_variable_get( var_name ).send(:+, 1) )
puts @a  # 3

Answer 2

See the below :

p 4.respond_to?(:"+=") #  false
p 4.respond_to?(:"=")  #  false
p 4.respond_to?(:"+")  #  true

a+=1 is syntactic sugar of a = a+1. But there is no direct method +=. = is an assignment operator,not the method as well. On the other hand Object#send takes method name as its argument. Thus your code will not work,the way you are looking for.