array = ["a","b","c"] # => ["a", "b", "c"] array[1] # => "b" array.fetch 1 # => "b" # ================================================== # # So far, so fine. # ================================================== # array[666] # => nil array.fetch 666 IndexError: index 666 out of array from (irb):5:in `fetch' from (irb):5
This may seem like a trival difference between the two, but
I am wondering in general why they behave differently.
Or in other words, why array[] does not return an error
whereas .fetch specifically does.
You might say that's the purpose of fetch, to raise an exception for
out-of-bounds indexes when [] just returns nil. Pick the method you want
depending on the error handling you want.
fetch is more general; if you want it to behave like []() in this case,
say array.fetch(666,nil)
PS:也可以指定fetch返回其他值
