Lists v. Tuples

Tuples

are placed in contiguous memory slots and behave like static data structures. they are not meant to change.

• meant for single data points that have a fixed number of elements
• memory usage is static and allocated upfront
• does NOT support insertion or deletion. any change requires a complete copy

iex(1)> tuple = {false, 1, 2, 3, false}

# use cases - key/value pair mappings
iex(3)> a = {:name, "Mark"}
iex(4)> b = {:rank, :general}

# which lends itself to Keyword lists
# in Elixir, Keyword Lists are syntactic sugar for a List
# with Tuples. so this:
iex(5)> kw_list = [name: "Mark", rank: :general]

# equals this:
iex(6)> list = [{:name, "Mark"}, {:rank, :general}]

# verify it with:
iex(7)> Enum.at(list, 0)
# => {:name, "Mark"}

how would this look in memory?

Lists

specifically in Elixir, are implemented as linked lists and are used to hold variable-length data. distributed arbitrarily, in no particular order, with each element holding a reference to the next one:

• supports insertion/deletion
• O(n) linear time
• fetching can be slow

iex(2)> list = [false, 1, 2, 3, false]

Links and Resources

How Elixir Lays Out Your Data in Memory - honeybadger

fantasic appsignal blog post here

…love this blog - openmymind