In Ruby, how can you invoke a method using its default argument or with a specified argument without repeating code?

Question

Say I have a ruby method:

def blah(foo=17)
   ...
end

In code I want to invoke blah with a specific argument "blah(a)" or invoke blah using its default argument "blah()" Is there any way to do that without specifying the method name twice? I'm trying to avoid:

if a.nil?
  blah()
else
  blah(a)
end

Because it makes the code look more complicated than it is. Best I can come up with (didn't test) is:

args=[]
args << a unless a.nil?
a.send :blah, args

Answer 1

I just tried a few ways, and didn't find any, but if you find yourself doing this a lot, I wonder of the benefit of using a default parameter that way. Try this instead:

def blah(foo=nil)
  foo ||= 17
  puts foo
end

blah()
a = nil
blah(a)
a = 20
blah(a)

This will output:

17
17
20

Answer 2

I don't like this answer, but I guess it works:

blah( *[a].compact )

Answer 3

I vote for

def blah(foo = nil)
    foo ||= 17
end

too.

But if you would like to distinguish nil-value and no-argument situation, I suggest using block, like this:

def blah
    foo = block_given? ? yield : 17
end

blah         #=> 17
blah { nil } #=> nil
blah { 71 }  #=> 71

Answer 4

In ruby everything has a return value. So if also has a return value. The following method works with any number of arguments. The * expands an array so the array elemnts are individual arguments.

blah(*
  if a.nil?
    []
  else
    [a]
  end
)

You don't have to indent it this way, but this looked like the indentation to make it clearest.

Answer 5

It's hard to say without knowing what the actual problem being solved is, but I have a feeling something like this would work best:

blah(a || 17)

This statement seems to more clearly express its intent, without leaving the reader to lookup the definition of the blah function in order to work out what the default is.