Add Char#printable? (#11429)

Co-authored-by: Jason Frey <[email protected]>

spec/std/char_spec.cr

@@ -390,6 +390,15 @@ describe "Char" do
     '酒'.ascii?.should be_false
   end
 
+  it "#printable?" do
+    ' '.printable?.should be_true
+    'a'.printable?.should be_true
+    '酒'.printable?.should be_true
+    '\n'.printable?.should be_false
+    '\e'.printable?.should be_false
+    '\uF8FF'.printable?.should be_false
+  end
+
   describe "clone" do
     it { 'a'.clone.should eq('a') }
   end

src/char.cr

@@ -489,11 +489,23 @@ struct Char
     ascii? ? ascii_control? : Unicode.control?(self)
   end
 
-  # Returns `true` if this is char is a mark character according to unicode.
+  # Returns `true` if this char is a mark character according to unicode.
   def mark? : Bool
     Unicode.mark?(self)
   end
 
+  # Returns `true` if this char is a printable character.
+  #
+  # There is no universal definition of printable characters in Unicode.
+  # For the purpose of this method, all characters with a visible glyph and the
+  # ASCII whitespace (` `) are considered printable.
+  #
+  # This means characters which are `control?` or `whitespace?` (except for ` `)
+  # are non-printable.
+  def printable?
+    !control? && (!whitespace? || self == ' ')
+  end
+
   # Returns this char as a string that contains a char literal.
   #
   # ```