私有方法`select'调用了nil：NilClass（NoMethodError）

Question

I am new to ruby and would love some help please :)

I fixed the error in my ruby code, but I'm confused as to WHY the fix works.

I get the following error private method `select' called for nil:NilClass (NoMethodError) when I type in the following line:

scanned = @keywords.select { |key| key.match(word) }

, which is located within the following method:

def find(word)
    return {} unless @entries.any?
    scanned = @keywords.select { |key| key.match(word) }
    found ={}
    if scanned.any? 
        scanned.each do |x| found.merge!( { x => @entries[x] } )
        end
    else
        {}
    end
    found
end

,yet this error goes away if I replace the erroneous line above with the following:

scanned = @entries.keys.sort.select { |key| key.match(word) }

I define @keywords as @keywords = @entries.keys.sort in the class structure below... Why can't I use '.select' on @keywords yet I can use it on @keywords' contents?

class Dictionary
def initialize
    @entries = {}
end

def entries
    @entries
end

def add(entry)
    @entries = entry.is_a?(Hash) ? @entries.merge!(entry) : @entries.merge!( {entry => nil} )
end

def keywords
    @keywords = @entries.keys.sort
end

def include?(keyword)
    @entries.keys.include?(keyword)
end

def find(word)
    return {} unless @entries.any?
    scanned = @keywords.select { |key| key.match(word) }
    found ={}
    if scanned.any? 
        scanned.each do |x| found.merge!( { x => @entries[x] } )
        end
    else
        {}
    end
    found
end

def printable
    printable = @entries.sort.map do |key, value| %Q{[#{key}] "#{value}"}
    end
    printable.join("\n")
end
end

Answer 1

You are never calling the method keywords , and thus, you are never executing the code that populates @keywords with data. It remains nil.

Answer 2

@keywords will remain nil until you call the method keywords , which will initialize @keywords to be the sorted entry keys.

It looks like you're calling find on a dictionary object without first calling keywords. This would result in a nil value for @keywords.