ruby - need help understanding this inject
I'd like to understand how the following code works:
def url
@url ||= {
"basename" => self.basename,
"output_ext" => self.output_ext,
}.inject("/:basename/") { |result, token|
result.gsub(/:#{token.first}/, token.last)
}.gsub(/\/\//, "/")
end
I know what it does; somehow it returns the url corresponding to a file located o a dir on a server. So it returns strings similar to this: /path/to/my/file.html
I understand that if @url
already has a value, it will be returned and the right ||=
will be discarded. I also understand that this begins creating a hash of two elements.
I also think I understand the last gsub; it replaces backslashes by slashes (to cope with windows servers, I guess).
What amazes me is the inject
part. I'm not able to understand it. I have used inject
before, but this one is too much for me. I don't see how this be done with an each
, sinc开发者_StackOverflow社区e I don't understand what it does.
I modified the original function slightly for this question; the original comes from this jekyll file.
Cheers!
foo.inject(bar) {|result, x| f(result,x) }
Can always be written as:
result = bar
foo.each {|x| result = f(result, x)}
result
So for your case, the version with each would look like this:
result = "/:basename/"
{
"basename" => self.basename,
"output_ext" => self.output_ext,
}.each {|token|
result = result.gsub(/:#{token.first}/, token.last)
}
result
Meaning: for all key-value-pairs in the hash, each occurrence of the key in the "/:basename/"
is replaced with the value.
Perhaps splitting the code and tweaking a little helps
options = { "basename" => self.basename, "output_ext" => self.output_ext }
options.inject("/:basename") do |result, key_and_kalue|
# Iterating over the hash yields an array of two elements, which I called key_and_value
result.gsub(":#{key_and_value[0]}", key_and_value[1])
end.gsub!(//\/\/, '/')
Basically, the inject code is iterating over all your options
and replacing for the actual value wherever it sees a ":key"
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