Ruby Calling a method based on an elseif statement

问题

So I'm still chugging along with learning how to code in Ruby and I've come across something new that I'm curious about. My teacher just started teaching us about methods and I was wondering if you could call/create a method based on an if-else statement. Like for example if you had a program that asked the user to type in someone's name could you then use that input to decide which method would be used?

example:

puts "Please enter name(Brian, Andy, Tod)"
string = gets.to_i
if string == "Brian"
   def b(string)
       puts "Hi Brian"
   return b

elsif string == "Andy"
   def a(string)
       puts "Hi Andy"
   return a

elsif string == "Tod"
   def t(string)
       puts "Hi Tod"
   return t
else
   puts "Not a valid entry"
end

I know that code likely does not work, I just created it off the top of my head to clarify what I meant, but is there actually a way to do this?

回答1:

Yeah, the normal way to do this is to define the methods beforehand then invoke them from the (elsif) conditional:

def b
  puts "Hello brian"
end

def a
  puts "Hello andy"
end

def t
  puts "Hello tod"
end

puts "Please enter name(Brian, Andy, Tod)"
string = gets.chomp
if string == "Brian"
   b
elsif string == "Andy"
   a
elsif string == "Tod"
   t
else
   puts "Not a valid entry"
end

when you say a by itself that's the same as saying a() - invoking the method. You could technically define the methods inside the conditional (before invoking them) but this isn't good style and is rarely done.

Some other points -

these methods don't use the string parameter so you can remove it, like I've done
gets.to_i is saying "get input and convert it to integer" - not what you want to do here. What you're looking for is gets.chomp, which gets a line of input and removes the \n newline character from the end (all gets input will have a newline character at the end)

Note this conditional chain seems like a good candidate for case, and you can refactor the puts into a single place -

def b
  "Hello brian"
end

def a
  "Hello andy"
end

def t
  "Hello tod"
end

input = gets.chomp
puts case input
when "Brian" then b
when "Andy" then a
when "Tod" then t
else "not a valid entry"
end

or you could use a hash structure instead of methods

puts {
  "Brian" => "Hello brian",
  "Andy" => "Hello andy",
  "Tod" => "Hello tod"
}.fetch(gets.chomp, "Invalid input")

来源：https://stackoverflow.com/questions/40478655/ruby-calling-a-method-based-on-an-elseif-statement

标签

ruby

if-statement

methods