<=> to determine version newer or older?

[thomthom]

Say, you want to do a version check to detect if a given module is the required minimum and alert the user if it is not.

Is this safe? Using and array with the version number and the <=> operator? Or is there some logic flaw here which might make the check fail?

<span class="syntaxdefault">minimum </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">[</span><span class="syntaxdefault"> 1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">2</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">0 </span><span class="syntaxkeyword">]<br /></span><span class="syntaxdefault">version </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">[</span><span class="syntaxdefault"> 1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">1</span><span class="syntaxkeyword">,</span><span class="syntaxdefault">20 </span><span class="syntaxkeyword">]<br /></span><span class="syntaxdefault">if minimum </span><span class="syntaxkeyword"><=></span><span class="syntaxdefault"> version </span><span class="syntaxkeyword">==</span><span class="syntaxdefault"> 1<br />  UI</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">messagebox</span><span class="syntaxkeyword">(</span><span class="syntaxdefault"> </span><span class="syntaxstring">'Sad Panda ;('</span><span class="syntaxdefault"> </span><span class="syntaxkeyword">)<br /></span><span class="syntaxdefault">end<br /></span>

[Dan Rathbun]

You cannot make numeric literals with more than 1 decimal point:
min = 1.2.3 Error: #<SyntaxError: (eval): compile error (eval): no .<digit> floating literal anymore; put 0 before dot

[Dan Rathbun]

I think this is safest:

module SomeLib
  VERSION = "1.2.3"
  VERSA   = VERSION.split('.').map{|i| i = i.to_i }
end

begin
  require("SomePath/to/SomeLib.rb")
  if defined?(SomeLib)
    minver = [1,2,5]
    if minver < SomeLib;;VERSA
      msg = "This plugin requires SomeLib version #{minver.join('.')} or higher."
      msg<< "      \n\nCurrent installed SomeLib version is; #{SomeLib;;VERSION}\n"
      UI.messagebox(msg)
      exit(0)
    end
  end
rescue Exception => e
  # catch SystemExit or LoadError here
else
  # no errors, load the plugin;
  require("ThisPath/to/ThisPlugin.rb")
end

[thomthom]

@dan rathbun said:

You cannot make numeric literals with more than 1 decimal point:
min = 1.2.3 Error: #<SyntaxError: (eval): compile error (eval): no .<digit> floating literal anymore; put 0 before dot

My bad, I typed . instead of , when posting the example...

[Dan Rathbun]

It is traditional in Ruby for VERSION constants to be a String of form "major.minor.teeny" (that should follow the RubyGems standard for use*****.)

But comparing numeric strings can cause collating problems, so usually yes you make a array copy, using integer members (which is faster for comparison anyhow.)

***** The RubyGems standard for version number use:

major = change in Compatibility

minor = change in Functionality, but not Compatibility

teeny = no change in intended Functionality, or Compatibility
(ie.. bug fix, typo fix, documentation fix, etc.)

[thomthom]

But given the example in my OP, <=> does seem to return correct value indicating "newer" or "older". From my tests it seemed to work fine...

[Dan Rathbun]

Of course it does.. it HAS to. <, >, >= etc (for classes that mix in Comparable,) will not work, unless <=> is first defined.

But there is subtle issue here. That is that the members of your array are Integer class, which are immediate objects.
It may be a different story if the members of the array were non-immediate strings with numerical characters.

[Dan Rathbun]

@thomthom said:

But given the example in my OP, <=> does seem to return correct value indicating "newer" or "older". From my tests it seemed to work fine...

I suppose it does not matter speedwise..

if minimum <=> version == 1
is actually doing an extra unneeded method call, than:
unless version >= minimum

[thomthom]

Oh, that works as well...

And I've been comparing each value by itself when putting it all in an array works just as easy...