October 2014
Intermediate to advanced
280 pages
7h 20m
English
Content preview from Programming Elixir
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Updating a Map
In the previous chapter we saw how lists are updated through a combination of copying and changing the head.
With maps, we can add new key/value entries and update existing entries without traversing the whole structure. But as with all values in Elixir, a map is immutable, and so the result of the update is a new map.
The simplest way to update a map is with this syntax:
| | new_map = %{ old_map | key => value, … } |
This creates a new map that is a copy of the old, but the values associated with the keys on the right of the pipe character are updated:
| | iex> m = %{ a: 1, b: 2, c: 3 } |
| | %{a: 1, b: 2, c: 3} |
| | iex> m1 = %{ m | b: "two", c: "three" } |
| | %{a: 1, b: "two", c: "three"} |
| | iex> m2 = %{ m1 | a: "one" } |
| | %{a: ... |
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