Merge pull request rubyworks#78 from u2/master

Add String#number? method.

lib/core/facets/string.rb

@@ -31,6 +31,7 @@
 require_relative 'string/natcmp.rb'
 require_relative 'string/nchar.rb'
 require_relative 'string/newlines.rb'
+require_relative 'string/number.rb'
 require_relative 'string/op_div.rb'
 require_relative 'string/op_sub.rb'          # included in `remove`.
 require_relative 'string/outdent.rb'

lib/core/facets/string/number.rb

@@ -0,0 +1,14 @@
+class String
+
+  # Returns true if it's a decimal digits.
+  #
+  #   "123_456_789_123_456_789.123_456_000_111".number?  # => true
+  #   "1.23".number?  # => true
+  #   "1.23a".number? # => false
+  #
+  # CREDIT: u2
+
+  def number?
+    !!self.match(/\A[+-]?\d+?(_?\d+?)*?(\.\d+(_?\d+?)*?)?\Z/)
+  end
+end

test/core/string/test_number.rb

@@ -0,0 +1,44 @@
+covers 'facets/string/number'
+
+test_case String do
+
+  method :number? do
+
+    test do
+      x = "1.23\n"
+      x.number?.assert == true
+    end
+
+    test do
+      x = "123_456_789_123_456_789.123_456_000_111\n"
+      x.number?.assert == true
+    end
+
+    test do
+      x = ".123\n"
+      x.number?.assert == false
+    end
+
+    test do
+      x = "123_\n"
+      x.number?.assert == false
+    end
+
+    test do
+      x = "_123\n"
+      x.number?.assert == false
+    end
+
+    test do
+      x = "23_456_789_123_456_.245\n"
+      x.number?.assert == false
+    end
+
+    test do
+      x = "23_456_789_123_456._245\n"
+      x.number?.assert == false
+    end
+
+  end
+
+end