有没有更优雅的方法来执行多重包含？ 选择红宝石？

Question

I came across this issue in a project last night, while writing a helper to pick an icon depending on a file extension, and was wondering if there was a better (more "ruby") way of handling it?

The code currently goes something like:

def choose_icon(myfile)
  icon = "default-icon"
  if ["*.doc","*.docx",".txt","*.dot"].include? File.extname(myfile)
    icon = "doc-icon"
  end
  if ["*.xls","*.xlsx","*.xlt"].include? File.extname(myfile)
    icon = "sheet-icon"
  end
  if ["*.mp3","*.aac","*.aiff","*.wav"].include? File.extname(myfile)
    icon = "audio-icon"
  end
  if ["*.mov","*.m4a","*.wmv"].include? File.extname(myfile)
    icon = "movie-icon"
  end
  icon # return the chosen icon
end

This somehow feels a little clumsy and inelegant to me, and I was struggling to find a better way to do it in Ruby.

(Note: The above example is REALLY simplified and the actual code is far longer and looks far more untidy.)

It would be really cool if the ' case ' construct would work like this:

def choose_icon(myfile)
  case File.extname(myfile)
  when ["*.doc","*.docx",".txt","*.dot"].include? 
    "doc-icon"
  when ["*.xls","*.xlsx","*.xlt"].include? 
    "sheet-icon"
  when ["*.mp3","*.aac","*.aiff","*.wav"].include? 
    "audio-icon"
  when ["*.mov","*.m4a","*.wmv"].include? 
    "movie-icon"
  else
    "default-icon"
  end
end

But of course, that doesn't work. It is so much easier to read though, so I was wondering if I had missed some other method of doing a multiple comparison against a collection of options that would restore some elegance and readability to my code?

Answer 1

You almost got it right. Just leave off the square brackets and the include? and it will work. I think the asterisks should not be necessary either since File.extname returns the extension with just a dot.

def choose_icon(myfile)
  case File.extname(myfile)
  when '.doc', '.docx', '.txt', '.dot'
    'doc-icon'
  when '.xls', '.xlsx', '.xlt' 
    'sheet-icon'
  when '.mp3', '.aac', '.aiff', '.wav'
    'audio-icon'
  when '.mov', '.m4a', '.wmv'
    'movie-icon'
  else
    'default-icon'
  end
end

Answer 2

You could use a hash:

h = [*(%w| .doc .docx .txt .dot |).product(["doc-icon"]),
     *(%w| .xls .xlsx .xlt      |).product(["sheet-icon"]),
     *(%w| .aac .aiff .wav      |).product(["audio-icon"]),
     *(%w| .mov .m4a  .wmv      |).product(["movie-icon"])].to_h
  #=> {".doc"=>"default-icon", ".docx"=>"default-icon",
  #    ".txt"=>"default-icon", ".dot"=>"default-icon",
  #    ".xls"=>"sheet-icon"  , ".xlsx"=>"sheet-icon",
  #    ".xlt"=>"sheet-icon"  , ".aac"=>"audio-icon",
  #    ".aiff"=>"audio-icon" , ".wav"=>"audio-icon",
  #    ".mov"=>"movie-icon"  , ".m4a"=>"movie-icon",
  #    ".wmv"=>"movie-icon"}
h.default = "default-icon"

h[File.extname("myfile.wav")]
  #=> "audio-icon"
h[File.extname("./mydir/myfile.abc")]
  #=> "default-icon"