I'm trying to send a parameter to a Ruby proc
p1 = [54, 21, 45, 76, 12, 11, 67, 5]
qualify = proc { |age, other| age > other }
puts p1.select(&qualify(30))
This is the error I get:
undefined method `qualify' for main:Object
age comes from the iteration of the array, and I want to have that last parameter (30) to get into the proc.
Is a proc the right tool to be using for this? I'm new to proc. I'm unclear how to get that parameter in there.
In order to use qualify in as select predicate, you need to reduce its arity (number of accepted arguments) through partial application. In other words - you need a new proc that would have other set to 30. It can be done with Method#curry, but it requires changing order of parameters:
qualify = proc { |other, age| age > other }
qualify.curry.call(30).call(10)
# => false
qualify.curry.call(30).call(40)
#=> true
I order to be able to pass this proc to select using &, you need to assign it so that it's available in the main object, e.g. by assigning it to an instance variable:
@qualify_30 = qualify.curry.call(30)
Now you can call:
p1.select{ |age| @qualify_30.call(age) }
# => [54, 45, 76, 67]
or:
p1.select(&@qualify_30)
# => [54, 45, 76, 67]
or inline:
p1.select(&qualify.curry.call(30))
# => [54, 45, 76, 67]
p1.select(&@qualify_30) or it could be done inline like p1.select(&qualify.curry.call(30))
@qualify_30[40] where [] is an alias to call.The easy way is to shuffle up how you define this:
p1 = [54, 21, 45, 76, 12, 11, 67, 5]
qualify = proc { |age| age > 30 }
puts p1.select(&qualify).join(',')
By moving the 30 into the qualify proc you've baked in the condition, it's no longer dynamic. Remember, the only methods that can be used with the shorthand &: trick are zero-argument ones, or single argument ones with & on a proc.
You could also use a closure to have the comparison variable exposed:
p1 = [54, 21, 45, 76, 12, 11, 67, 5]
required = 30
qualify = proc { |age| age > required }
puts p1.select(&qualify).join(',')
required = 10
puts p1.select(&qualify).join(',')
The better way is to just spell it out, that's what Ruby is all about. Here in a more idiomatic form:
p1 = [54, 21, 45, 76, 12, 11, 67, 5]
puts p1.select { |age| age > 30 }
The only reason for an intermediate Proc is if you'd want to, for some reason, save that somewhere and re-use it later.
qualify here has arity of 1. And it's not even a method. Perhaps, this assertion can be reworded somehow.& doesn't see the method call. Only its result. repl.it/repls/EuphoricPunctualBetatest
parameter, so that really is just another hard coded proc as I see it. Doesn't really respect DRY. I assumed it would be easy to throw in the param.Use the select statement in the proc itself, so that the proc would calculate and return an array.
2.1.5 :119 > qualify = proc { |age_array, age_limit| age_array.select { |age| age > age_limit } }
=> #<Proc:0xe7bc2cc@(irb):119>
2.1.5 :120 >
2.1.5 :121 >
2.1.5 :122 > qualify.call(p1, 30)
=> [54, 45, 76, 67]
procsthat I can throwparamsat.procversion so I can learn them.