CODEWITHSUNDEEP
rubysyntax
Wojciech Danilo
Wojciech Danilo

Reputation: 11803

Ruby method parameters?

I'm new to Ruby and I'm completely disgusted. Why does the following code:

def some_method(v=1) 10*v end

puts (some_method (1).next)
puts  some_method (1).next

Evaluate to:

20
11

Upvotes: 2

Views: 188

Answers (3)

Jakob S
Jakob S

Reputation: 20125

In Ruby 1.8.7, the first example evaluates to 20, because that is the correct behavior.

Let's break it down. We start with

puts (some_method (1).next)

We then add the missing/implicit parentheses:

puts((some_method((1).next)))

Let's split this out a bit into its separate parts:

puts(
  (
    some_method(
      (1).next
    )
  )
)

Ruby starts from the inside, evaluating (1). The value of that is, well, 1, so we get

puts(
  (
    some_method(
      1.next
    )
  )
)

Next up, 1.next, which returns 2:

puts(
  (
    some_method(
      2
    )
  )
)

Thus, Ruby passes 2 as the parameter to some_method, which then multiplies by 10 and returns the correct value, 20:

puts(
  (
    20
  )
)

This - unsurprisingly outputs 20.

What you probably wanted to write is

puts some_method(1).next

which outputs 11. The space you've added between the method name and the parenthesis is significant.

Interestingly, if you are indeed running 1.8.7, you actually get a warning in that last example of yours:

>> puts some_method (1).next
(irb):13: warning: don't put space before argument parentheses
11
=> nil

Upvotes: 5

mcfinnigan
mcfinnigan

Reputation: 11638

Under jruby-1.6.7.2 in ruby 1.8 compatibility mode, I see:

20
11

Whereas in 1.9 compatibility mode I see

20
20

I suspect that there was a change to the precedence operators.

Upvotes: 1

Matthias
Matthias

Reputation: 4375

# first case
puts (some_method (1).next)

=> through the () around some_method (1).next everything gets wrapped into the puts.

some_method (1).next => (1).next => 2 => 2*10 => 20

# second case
puts some_method (1).next

=> here is no "wrapper" around the puts

some_method (1).next => 1*10 => 10 => 10.next => 11

UPDATE: (ruby 1.9.2-p290)

Interesting difference between "with space" and "without space" (okay, that´s no answer, that´s another question I think :))

irb(main):011:0> puts some_method (1).next
20
=> nil
irb(main):012:0> puts some_method(1).next
11
=> nil

Upvotes: 1

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