Refactor letter options for index

Avoid code repetition and add comment.

Although we didn't have time to implement it, this was suggested during
The Biggest Mobprogramming session ever at RubyConfBY 2019:
https://rubyconference.by

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1 files changed, 7 insertions, 10 deletions

diff --git a/lib/highline/menu.rb b/lib/highline/menu.rb
index 4db6cd2..42be9bd 100755
--- a/lib/highline/menu.rb
+++ b/lib/highline/menu.rb
@@ -374,12 +374,10 @@ class HighLine
     end
 
     def map_items_by_index
-      if @index == :letter
-        l_index = "`"
-        all_items.map { l_index.succ!.dup }
-      elsif @index == :capital_letter
-        l_index = "@"
-        all_items.map { l_index.succ!.dup }
+      if [:letter, :capital_letter].include?(@index)
+        # @ and ` are the previous ASCII characters to A and a respectively
+        prev_char = (@index == :capital_letter ? '@' : '`')
+        all_items.map { prev_char.succ!.dup }
       else
         (1..all_items.size).map(&:to_s)
       end
@@ -520,10 +518,9 @@ class HighLine
       case @index
       when :number
         ["#{ix + 1}#{@index_suffix}", text]
-      when :letter
-        ["#{('a'.ord + ix).chr}#{@index_suffix}", text]
-      when :capital_letter
-        ["#{('A'.ord + ix).chr}#{@index_suffix}", text]
+      when :letter, :capital_letter
+        first_letter = (@index == :capital_letter ? 'A' : 'a')
+        ["#{(first_letter.ord + ix).chr}#{@index_suffix}", text]
       when :none
         [text, ""]
       else