Add Gather Positional Arguments In Method Definition as a Ruby TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1514 TILs and counting..._
+_1515 TILs and counting..._
 
 ---
 
@@ -1225,6 +1225,7 @@ _1514 TILs and counting..._
 - [Finding The Source of Ruby Methods](ruby/finding-the-source-of-ruby-methods.md)
 - [Format A Hash Into A String Template](ruby/format-a-hash-into-a-string-template.md)
 - [Forward All Arguments To Another Method](ruby/forward-all-arguments-to-another-method.md)
+- [Gather Positional Arguments In Method Definition](ruby/gather-positional-arguments-in-method-definition.md)
 - [Generate A Signed JWT Token](ruby/generate-a-signed-jwt-token.md)
 - [Generate Ruby Version And Gemset Files With RVM](ruby/generate-ruby-version-and-gemset-files-with-rvm.md)
 - [Get Info About Your RubyGems Environment](ruby/get-info-about-your-ruby-gems-environment.md)

ruby/gather-positional-arguments-in-method-definition.md

@@ -0,0 +1,55 @@
+# Gather Positional Arguments In Method Definition
+
+The `*` symbol can be used in Ruby in a method definition to gather up an
+arbitrary number of positional arguments.
+
+For instance, we can gather all positional arguments with this method
+definition:
+
+```ruby
+def gather_all(*args)
+  puts args
+end
+```
+
+Or we can isolate the first positional arg and then gather the rest:
+
+```ruby
+def first_and_rest(first, *rest)
+  puts "First: #{first}, Rest: #{rest}"
+end
+```
+
+We can even do something a bit more interesting like isolating the first and
+last arguments while gathering up everything else in the middle:
+
+```ruby
+def pop_parens(left, *middle, right)
+  if left != '(' || right != ')'
+    raise "Uh oh!"
+  else
+    if middle.size == 1
+      puts "Found: #{middle.first}"
+    else
+      pop_parens(*middle)
+    end
+  end
+end
+```
+
+Here is what it looks like if we splat some different sets of arguments into
+that method call:
+
+```ruby
+> tokens1 = "((((4))))".split('')
+=> ["(", "(", "(", "(", "4", ")", ")", ")", ")"]
+> tokens2 = "((4))))".split('')
+=> ["(", "(", "4", ")", ")", ")", ")"]
+> pop_parens(*tokens1)
+Found: 4
+=> nil
+> pop_parens(*tokens2)
+(irb):87:in `pop_parens': Uh oh! (RuntimeError)
+```
+
+[source](https://ruby-doc.org/3.3.6/syntax/methods_rdoc.html#label-Array-2FHash+Argument)