Add reduce vs each with index note

src/SUMMARY.md

@@ -17,6 +17,7 @@
     - [Testing](./dev/rust/testing.md)
   - [Ruby](./dev/ruby/main.md)
     - [arrays](./dev/ruby/arrays.md)
+    - [reduce vs each_with_object](./dev/ruby/reduce_vs_each_with_object.md)
   - [TypeScript](./dev/ts/main.md)
     - [interfaces](./dev/ts/interfaces.md)
     - [decorators](./dev/ts/decorators.md)

src/dev/ruby/reduce_vs_each_with_object.md

@@ -0,0 +1,38 @@
+# Reduce vs Each With Object
+
+Both methods serve the same purpose : from an Enumerator create a single value
+out of it
+
+## Reduce
+
+Reduce is prefered when you need to produce a simple value because it reduce over the returned value
+
+```ruby
+[1, 2, 3].reduce(:+)
+> 3
+```
+
+We can illustrate this simply with this snippet :
+
+```ruby
+[1, 2, 3].reduce do |acc, v|
+  acc += v
+  0
+end
+> 0
+```
+
+## Each With Object
+
+Each with object is prefered when you reduce on a hash or some sort of complex
+object beacause is use the accumulator value and not the returned one
+
+```ruby
+[1, 2, 3].each_with_object({ sum: 0 }) do |v, acc|
+  acc[:sum] += v
+  0
+end
+> {sum: 6}
+```
+
+**Fun fact**, `reduce` takes `|acc, v|` while `each_with_object` take `|v, acc|`