Undefined method 'array' for main:Object

Question

So I was just playing with blocks in ruby, and I wrote this code:

#!/usr/bin/env ruby

def my_map ary
    a = ary.clone
    if block_given?
        while element = a.shift
            yield element
        end
    else
        ary
    end
end

array = [1, 2, 3, 4, 5]

my_map array { |e|
    puts e * 2
}

p array

But it keeps giving me this error:

./tests.rb:16:in `<main>': undefined method `array' for main:Object (NoMethodError)

Why is that? I can clearly see that I defined array. I would appreciate any help, thanks!

bjhaid · Accepted Answer · 2014-03-12 01:20:26Z

2

The Ruby interpreter parses:

my_map array { |e|
    puts e * 2
}

as:

my_map(array ( { |e| puts e * 2 } ) )

which explains, why it thinks array should be a method, to avoid that change:

my_map array { |e|
    puts e * 2
}

to:

my_map(array) { |e|
    puts e * 2
}

or:

my_map array do |e|
    puts e * 2
end

the curly braces are meant for one-liner blocks and should be avoided for multi-line blocks

edited Mar 12, 2014 at 1:20

answered Mar 12, 2014 at 1:04

bjhaid

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3 Comments

tadman Over a year ago

Since { is used for both hashes and blocks, the parser can get tripped up if it doesn't know which one to expect.

bjhaid Over a year ago

@tadman it does not expect a hash, as an hash there would come as an argument which does not occur without a comma

tadman Over a year ago

Ah, right, it's parsing as my_map(array { |e| ... }) vs. the expected my_map(array) { |e| ... }. I tend to use brackets pretty rigorously to avoid this ambiguity.

Rafa Paez · Accepted Answer · 2014-03-12 01:15:35Z

0

When passing an argument and a multi-line block, you have to put the argument between braces

my_map(array) { |e|
  puts e * 2
}

or use a do end block

my_map array do |e|
  puts e * 2
end

Anyway this one-line block looks the best approach for this case:

my_map(array) { |e| puts e * 2 }

edited Mar 12, 2014 at 1:15

answered Mar 12, 2014 at 1:05

Rafa Paez

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1 Comment

bjhaid Over a year ago

the one-liner would fail if the params is not in parens

bjhaid · Accepted Answer · 2014-03-12 01:17:20Z

0

this should work:

my_map(array) { |e|
    puts e * 2
}

edited Mar 12, 2014 at 1:17

bjhaid

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answered Mar 12, 2014 at 1:08

Tom

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