View Source Keyword (Elixir v1.17.2)

A keyword list is a list that consists exclusively of two-element tuples.

The first element of these tuples is known as the key, and it must be an atom. The second element, known as the value, can be any term.

Keywords are mostly used to work with optional values. For a general introduction to keywords and how the compare with maps, see our Keyword and Maps guide.

Examples

For example, the following is a keyword list:

[{:exit_on_close, true}, {:active, :once}, {:packet_size, 1024}]

Elixir provides a special and more concise syntax for keyword lists:

[exit_on_close: true, active: :once, packet_size: 1024]

The two syntaxes return the exact same value.

A key can be any atom, consisting of Unicode letters, numbers, an underscore or the @ sign. If the key should have any other characters, such as spaces, you can wrap it in quotes:

iex> ["exit on close": true]
["exit on close": true]

Wrapping an atom in quotes does not make it a string. Keyword list keys are always atoms. Quotes should only be used when necessary or Elixir will issue a warning.

Duplicate keys and ordering

A keyword may have duplicate keys so it is not strictly a key-value data type. However, most of the functions in this module work on a key-value structure and behave similar to the functions you would find in the Map module. For example, Keyword.get/3 will get the first entry matching the given key, regardless if duplicate entries exist. Similarly, Keyword.put/3 and Keyword.delete/2 ensure all duplicate entries for a given key are removed when invoked. Note, however, that keyword list operations need to traverse the whole list in order to find keys, so these operations are slower than their map counterparts.

A handful of functions exist to handle duplicate keys, for example, get_values/2 returns all values for a given key and delete_first/2 deletes just the first entry of the existing ones.

Even though lists preserve the existing order, the functions in Keyword do not guarantee any ordering. For example, if you invoke Keyword.put(opts, new_key, new_value), there is no guarantee for where new_key will be added to (the front, the end or anywhere else).

Given ordering is not guaranteed, it is not recommended to pattern match on keyword lists either. For example, a function such as:

def my_function([some_key: value, another_key: another_value])

will match

my_function([some_key: :foo, another_key: :bar])

but it won't match

my_function([another_key: :bar, some_key: :foo])

Most of the functions in this module work in linear time. This means that the time it takes to perform an operation grows at the same rate as the length of the list.

Call syntax

When keyword lists are passed as the last argument to a function, the square brackets around the keyword list can be omitted. For example, the keyword list syntax:

String.split("1-0", "-", [trim: true, parts: 2])

can be written without the enclosing brackets whenever it is the last argument of a function call:

String.split("1-0", "-", trim: true, parts: 2)

Since tuples, lists and maps are treated similarly to function arguments in Elixir syntax, this property is also available to them:

iex> {1, 2, foo: :bar}
{1, 2, [{:foo, :bar}]}

iex> [1, 2, foo: :bar]
[1, 2, {:foo, :bar}]

iex> %{1 => 2, foo: :bar}
%{1 => 2, :foo => :bar}

Summary

Functions

Deletes the entries in the keyword list under a specific key.

Deletes the first entry in the keyword list under a specific key.

Drops the given keys from the keyword list.

Checks if two keywords are equal.

Fetches the value for a specific key and returns it in a tuple.

Fetches the value for specific key.

Returns a keyword list containing only the entries from keywords for which the function fun returns a truthy value.

Builds a keyword from the given keys and the fixed value.

Gets the value under the given key.

Gets the value from key and updates it, all in one pass.

Gets the value under key and updates it. Raises if there is no key.

Gets the value under the given key.

Gets all values under a specific key.

Returns whether a given key exists in the given keywords.

Intersects two keyword lists, returning a keyword with the common keys.

Returns all keys from the keyword list.

Returns true if term is a keyword list, otherwise false.

Merges two keyword lists into one.

Merges two keyword lists into one.

Returns an empty keyword list, i.e. an empty list.

Creates a keyword list from an enumerable.

Creates a keyword list from an enumerable via the transformation function.

Returns the first value for key and removes all associated entries in the keyword list.

Returns the first value for key and removes all associated entries in the keyword list, raising if key is not present.

Returns and removes the first value associated with key in the keyword list.

Lazily returns and removes all values associated with key in the keyword list.

Returns all values for key and removes all associated entries in the keyword list.

Puts the given value under the specified key.

Puts the given value under key, unless the entry key already exists.

Evaluates fun and puts the result under key in keyword list unless key is already present.

Returns a keyword list excluding the entries from keywords for which the function fun returns a truthy value.

Puts a value under key only if the key already exists in keywords.

Puts a value under key only if the key already exists in keywords.

Replaces the value under key using the given function only if key already exists in keywords.

Takes all entries corresponding to the given keys and extracts them into a separate keyword list.

Splits the keywords into two keyword lists according to the given function fun.

Takes all entries corresponding to the given keys and returns them as a new keyword list.

Returns the keyword list itself.

Updates the value under key in keywords using the given function.

Updates the value under key using the given function.

Ensures the given keyword has only the keys given in values.

Similar to validate/2 but returns the keyword or raises an error.

Returns all values from the keyword list.

Types

Link to this type

default()

View Source (since 1.17.0)
@type default() :: any()
@type key() :: atom()
@type t() :: [{key(), value()}]
@type t(value) :: [{key(), value}]
@type value() :: any()

Functions

@spec delete(t(), key()) :: t()

Deletes the entries in the keyword list under a specific key.

If the key does not exist, it returns the keyword list unchanged. Use delete_first/2 to delete just the first entry in case of duplicate keys.

Examples

iex> Keyword.delete([a: 1, b: 2], :a)
[b: 2]
iex> Keyword.delete([a: 1, b: 2, a: 3], :a)
[b: 2]
iex> Keyword.delete([b: 2], :a)
[b: 2]
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delete_first(keywords, key)

View Source
@spec delete_first(t(), key()) :: t()

Deletes the first entry in the keyword list under a specific key.

If the key does not exist, it returns the keyword list unchanged.

Examples

iex> Keyword.delete_first([a: 1, b: 2, a: 3], :a)
[b: 2, a: 3]
iex> Keyword.delete_first([b: 2], :a)
[b: 2]
@spec drop(t(), [key()]) :: t()

Drops the given keys from the keyword list.

Removes duplicate keys from the new keyword list.

Examples

iex> Keyword.drop([a: 1, a: 2], [:a])
[]
iex> Keyword.drop([a: 1, b: 2, c: 3], [:b, :d])
[a: 1, c: 3]
iex> Keyword.drop([a: 1, b: 2, b: 3, c: 3, a: 5], [:b, :d])
[a: 1, c: 3, a: 5]
@spec equal?(t(), t()) :: boolean()

Checks if two keywords are equal.

Considers two keywords to be equal if they contain the same keys and those keys contain the same values.

Examples

iex> Keyword.equal?([a: 1, b: 2], [b: 2, a: 1])
true
iex> Keyword.equal?([a: 1, b: 2], [b: 1, a: 2])
false
iex> Keyword.equal?([a: 1, b: 2, a: 3], [b: 2, a: 3, a: 1])
true

Comparison between values is done with ===/3, which means integers are not equivalent to floats:

iex> Keyword.equal?([a: 1.0], [a: 1])
false
@spec fetch(t(), key()) :: {:ok, value()} | :error

Fetches the value for a specific key and returns it in a tuple.

If the key does not exist, it returns :error.

Examples

iex> Keyword.fetch([a: 1], :a)
{:ok, 1}
iex> Keyword.fetch([a: 1], :b)
:error
@spec fetch!(t(), key()) :: value()

Fetches the value for specific key.

If the key does not exist, it raises a KeyError.

Examples

iex> Keyword.fetch!([a: 1], :a)
1
iex> Keyword.fetch!([a: 1], :b)
** (KeyError) key :b not found in: [a: 1]
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filter(keywords, fun)

View Source (since 1.13.0)
@spec filter(t(), ({key(), value()} -> as_boolean(term()))) :: t()

Returns a keyword list containing only the entries from keywords for which the function fun returns a truthy value.

See also reject/2 which discards all entries where the function returns a truthy value.

Examples

iex> Keyword.filter([one: 1, two: 2, three: 3], fn {_key, val} -> rem(val, 2) == 1 end)
[one: 1, three: 3]
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from_keys(keys, value)

View Source (since 1.14.0)
@spec from_keys([key()], value()) :: t(value())

Builds a keyword from the given keys and the fixed value.

Examples

iex> Keyword.from_keys([:foo, :bar, :baz], :atom)
[foo: :atom, bar: :atom, baz: :atom]
iex> Keyword.from_keys([], :atom)
[]
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get(keywords, key, default \\ nil)

View Source
@spec get(t(), key(), default()) :: value() | default()

Gets the value under the given key.

Returns the default value if key does not exist (nil if no default value is provided).

If duplicate entries exist, it returns the first one. Use get_values/2 to retrieve all entries.

Examples

iex> Keyword.get([], :a)
nil
iex> Keyword.get([a: 1], :a)
1
iex> Keyword.get([a: 1], :b)
nil
iex> Keyword.get([a: 1], :b, 3)
3

With duplicate keys:

iex> Keyword.get([a: 1, a: 2], :a, 3)
1
iex> Keyword.get([a: 1, a: 2], :b, 3)
3
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get_and_update(keywords, key, fun)

View Source
@spec get_and_update(t(), key(), (value() | nil ->
                              {current_value, new_value :: value()} | :pop)) ::
  {current_value, new_keywords :: t()}
when current_value: value()

Gets the value from key and updates it, all in one pass.

The fun argument receives the value of key (or nil if key is not present) and must return a two-element tuple: the current value (the retrieved value, which can be operated on before being returned) and the new value to be stored under key. The fun may also return :pop, implying the current value shall be removed from the keyword list and returned.

Returns a tuple that contains the current value returned by fun and a new keyword list with the updated value under key.

Examples

iex> Keyword.get_and_update([a: 1], :a, fn current_value ->
...>   {current_value, "new value!"}
...> end)
{1, [a: "new value!"]}

iex> Keyword.get_and_update([a: 1], :b, fn current_value ->
...>   {current_value, "new value!"}
...> end)
{nil, [b: "new value!", a: 1]}

iex> Keyword.get_and_update([a: 2], :a, fn number ->
...>   {2 * number, 3 * number}
...> end)
{4, [a: 6]}

iex> Keyword.get_and_update([a: 1], :a, fn _ -> :pop end)
{1, []}

iex> Keyword.get_and_update([a: 1], :b, fn _ -> :pop end)
{nil, [a: 1]}
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get_and_update!(keywords, key, fun)

View Source
@spec get_and_update!(t(), key(), (value() ->
                               {current_value, new_value :: value()} | :pop)) ::
  {current_value, new_keywords :: t()}
when current_value: value()

Gets the value under key and updates it. Raises if there is no key.

The fun argument receives the value under key and must return a two-element tuple: the current value (the retrieved value, which can be operated on before being returned) and the new value to be stored under key.

Returns a tuple that contains the current value returned by fun and a new keyword list with the updated value under key.

Examples

iex> Keyword.get_and_update!([a: 1], :a, fn current_value ->
...>   {current_value, "new value!"}
...> end)
{1, [a: "new value!"]}

iex> Keyword.get_and_update!([a: 1], :b, fn current_value ->
...>   {current_value, "new value!"}
...> end)
** (KeyError) key :b not found in: [a: 1]

iex> Keyword.get_and_update!([a: 1], :a, fn _ ->
...>   :pop
...> end)
{1, []}
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get_lazy(keywords, key, fun)

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@spec get_lazy(t(), key(), (-> value())) :: value()

Gets the value under the given key.

If key does not exist, lazily evaluates fun and returns its result.

This is useful if the default value is very expensive to calculate or generally difficult to set up and tear down again.

If duplicate entries exist, it returns the first one. Use get_values/2 to retrieve all entries.

Examples

iex> keyword = [a: 1]
iex> fun = fn ->
...>   # some expensive operation here
...>   13
...> end
iex> Keyword.get_lazy(keyword, :a, fun)
1
iex> Keyword.get_lazy(keyword, :b, fun)
13
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get_values(keywords, key)

View Source
@spec get_values(t(), key()) :: [value()]

Gets all values under a specific key.

Examples

iex> Keyword.get_values([], :a)
[]
iex> Keyword.get_values([a: 1], :a)
[1]
iex> Keyword.get_values([a: 1, a: 2], :a)
[1, 2]
@spec has_key?(t(), key()) :: boolean()

Returns whether a given key exists in the given keywords.

Examples

iex> Keyword.has_key?([a: 1], :a)
true
iex> Keyword.has_key?([a: 1], :b)
false
Link to this function

intersect(keyword1, keyword2, fun \\ fn _key, _v1, v2 -> v2 end)

View Source (since 1.17.0)
@spec intersect(keyword(), keyword(), (key(), value(), value() -> value())) ::
  keyword()

Intersects two keyword lists, returning a keyword with the common keys.

By default, it returns the values of the intersected keys in keyword2. The keys are returned in the order found in keyword1.

Examples

iex> Keyword.intersect([a: 1, b: 2], [b: "b", c: "c"])
[b: "b"]

iex> Keyword.intersect([a: 1, b: 2], [b: 2, c: 3], fn _k, v1, v2 ->
...>   v1 + v2
...> end)
[b: 4]
@spec keys(t()) :: [key()]

Returns all keys from the keyword list.

Keeps duplicate keys in the resulting list of keys.

Examples

iex> Keyword.keys(a: 1, b: 2)
[:a, :b]

iex> Keyword.keys(a: 1, b: 2, a: 3)
[:a, :b, :a]

iex> Keyword.keys([{:a, 1}, {"b", 2}, {:c, 3}])
** (ArgumentError) expected a keyword list, but an entry in the list is not a two-element tuple with an atom as its first element, got: {"b", 2}
@spec keyword?(term()) :: boolean()

Returns true if term is a keyword list, otherwise false.

When term is a list it is traversed to the end.

Examples

iex> Keyword.keyword?([])
true
iex> Keyword.keyword?(a: 1)
true
iex> Keyword.keyword?([{Foo, 1}])
true
iex> Keyword.keyword?([{}])
false
iex> Keyword.keyword?([:key])
false
iex> Keyword.keyword?(%{})
false
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merge(keywords1, keywords2)

View Source
@spec merge(t(), t()) :: t()

Merges two keyword lists into one.

Adds all keys, including duplicate keys, given in keywords2 to keywords1, overriding any existing ones.

There are no guarantees about the order of the keys in the returned keyword.

Examples

iex> Keyword.merge([a: 1, b: 2], [a: 3, d: 4])
[b: 2, a: 3, d: 4]

iex> Keyword.merge([a: 1, b: 2], [a: 3, d: 4, a: 5])
[b: 2, a: 3, d: 4, a: 5]

iex> Keyword.merge([a: 1], [2, 3])
** (ArgumentError) expected a keyword list as the second argument, got: [2, 3]
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merge(keywords1, keywords2, fun)

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@spec merge(t(), t(), (key(), value(), value() -> value())) :: t()

Merges two keyword lists into one.

Adds all keys, including duplicate keys, given in keywords2 to keywords1. Invokes the given function to solve conflicts.

If keywords2 has duplicate keys, it invokes the given function for each matching pair in keywords1.

There are no guarantees about the order of the keys in the returned keyword.

Examples

iex> Keyword.merge([a: 1, b: 2], [a: 3, d: 4], fn _k, v1, v2 ->
...>   v1 + v2
...> end)
[b: 2, a: 4, d: 4]

iex> Keyword.merge([a: 1, b: 2], [a: 3, d: 4, a: 5], fn :a, v1, v2 ->
...>   v1 + v2
...> end)
[b: 2, a: 4, d: 4, a: 5]

iex> Keyword.merge([a: 1, b: 2, a: 3], [a: 3, d: 4, a: 5], fn :a, v1, v2 ->
...>   v1 + v2
...> end)
[b: 2, a: 4, d: 4, a: 8]

iex> Keyword.merge([a: 1, b: 2], [:a, :b], fn :a, v1, v2 ->
...>   v1 + v2
...> end)
** (ArgumentError) expected a keyword list as the second argument, got: [:a, :b]
@spec new() :: []

Returns an empty keyword list, i.e. an empty list.

Examples

iex> Keyword.new()
[]
@spec new(Enumerable.t()) :: t()

Creates a keyword list from an enumerable.

Removes duplicate entries and the last one prevails. Unlike Enum.into(enumerable, []), Keyword.new(enumerable) guarantees the keys are unique.

Examples

iex> Keyword.new([{:b, 1}, {:a, 2}])
[b: 1, a: 2]

iex> Keyword.new([{:a, 1}, {:a, 2}, {:a, 3}])
[a: 3]
@spec new(Enumerable.t(), (term() -> {key(), value()})) :: t()

Creates a keyword list from an enumerable via the transformation function.

Removes duplicate entries and the last one prevails. Unlike Enum.into(enumerable, [], fun), Keyword.new(enumerable, fun) guarantees the keys are unique.

Examples

iex> Keyword.new([:a, :b], fn x -> {x, x} end)
[a: :a, b: :b]
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pop(keywords, key, default \\ nil)

View Source
@spec pop(t(), key(), default()) :: {value() | default(), t()}

Returns the first value for key and removes all associated entries in the keyword list.

It returns a tuple where the first element is the first value for key and the second element is a keyword list with all entries associated with key removed. If the key is not present in the keyword list, it returns {default, keyword_list}.

If you don't want to remove all the entries associated with key use pop_first/3 instead, which will remove only the first entry.

Examples

iex> Keyword.pop([a: 1], :a)
{1, []}
iex> Keyword.pop([a: 1], :b)
{nil, [a: 1]}
iex> Keyword.pop([a: 1], :b, 3)
{3, [a: 1]}
iex> Keyword.pop([a: 1, a: 2], :a)
{1, []}
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pop!(keywords, key)

View Source (since 1.10.0)
@spec pop!(t(), key()) :: {value(), t()}

Returns the first value for key and removes all associated entries in the keyword list, raising if key is not present.

This function behaves like pop/3, but raises in case the key is not present in the given keywords.

Examples

iex> Keyword.pop!([a: 1], :a)
{1, []}
iex> Keyword.pop!([a: 1, a: 2], :a)
{1, []}
iex> Keyword.pop!([a: 1], :b)
** (KeyError) key :b not found in: [a: 1]
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pop_first(keywords, key, default \\ nil)

View Source
@spec pop_first(t(), key(), default()) :: {value() | default(), t()}

Returns and removes the first value associated with key in the keyword list.

Keeps duplicate keys in the resulting keyword list.

Examples

iex> Keyword.pop_first([a: 1], :a)
{1, []}
iex> Keyword.pop_first([a: 1], :b)
{nil, [a: 1]}
iex> Keyword.pop_first([a: 1], :b, 3)
{3, [a: 1]}
iex> Keyword.pop_first([a: 1, a: 2], :a)
{1, [a: 2]}
Link to this function

pop_lazy(keywords, key, fun)

View Source
@spec pop_lazy(t(), key(), (-> value())) :: {value(), t()}

Lazily returns and removes all values associated with key in the keyword list.

This is useful if the default value is very expensive to calculate or generally difficult to set up and tear down again.

Removes all duplicate keys. See pop_first/3 for removing only the first entry.

Examples

iex> keyword = [a: 1]
iex> fun = fn ->
...>   # some expensive operation here
...>   13
...> end
iex> Keyword.pop_lazy(keyword, :a, fun)
{1, []}
iex> Keyword.pop_lazy(keyword, :b, fun)
{13, [a: 1]}
Link to this function

pop_values(keywords, key)

View Source (since 1.10.0)
@spec pop_values(t(), key()) :: {[value()], t()}

Returns all values for key and removes all associated entries in the keyword list.

It returns a tuple where the first element is a list of values for key and the second element is a keyword list with all entries associated with key removed. If the key is not present in the keyword list, it returns {[], keyword_list}.

If you don't want to remove all the entries associated with key use pop_first/3 instead, which will remove only the first entry.

Examples

iex> Keyword.pop_values([a: 1], :a)
{[1], []}
iex> Keyword.pop_values([a: 1], :b)
{[], [a: 1]}
iex> Keyword.pop_values([a: 1, a: 2], :a)
{[1, 2], []}
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put(keywords, key, value)

View Source
@spec put(t(), key(), value()) :: t()

Puts the given value under the specified key.

If a value under key already exists, it overrides the value and removes all duplicate entries.

Examples

iex> Keyword.put([a: 1], :b, 2)
[b: 2, a: 1]
iex> Keyword.put([a: 1, b: 2], :a, 3)
[a: 3, b: 2]
iex> Keyword.put([a: 1, b: 2, a: 4], :a, 3)
[a: 3, b: 2]
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put_new(keywords, key, value)

View Source
@spec put_new(t(), key(), value()) :: t()

Puts the given value under key, unless the entry key already exists.

Examples

iex> Keyword.put_new([a: 1], :b, 2)
[b: 2, a: 1]
iex> Keyword.put_new([a: 1, b: 2], :a, 3)
[a: 1, b: 2]
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put_new_lazy(keywords, key, fun)

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@spec put_new_lazy(t(), key(), (-> value())) :: t()

Evaluates fun and puts the result under key in keyword list unless key is already present.

This is useful if the value is very expensive to calculate or generally difficult to set up and tear down again.

Examples

iex> keyword = [a: 1]
iex> fun = fn ->
...>   # some expensive operation here
...>   13
...> end
iex> Keyword.put_new_lazy(keyword, :a, fun)
[a: 1]
iex> Keyword.put_new_lazy(keyword, :b, fun)
[b: 13, a: 1]
Link to this function

reject(keywords, fun)

View Source (since 1.13.0)
@spec reject(t(), ({key(), value()} -> as_boolean(term()))) :: t()

Returns a keyword list excluding the entries from keywords for which the function fun returns a truthy value.

See also filter/2.

Examples

iex> Keyword.reject([one: 1, two: 2, three: 3], fn {_key, val} -> rem(val, 2) == 1 end)
[two: 2]
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replace(keywords, key, value)

View Source (since 1.11.0)
@spec replace(t(), key(), value()) :: t()

Puts a value under key only if the key already exists in keywords.

In case a key exists multiple times in the keyword list, it removes later occurrences.

Examples

iex> Keyword.replace([a: 1, b: 2, a: 4], :a, 3)
[a: 3, b: 2]

iex> Keyword.replace([a: 1], :b, 2)
[a: 1]
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replace!(keywords, key, value)

View Source (since 1.5.0)
@spec replace!(t(), key(), value()) :: t()

Puts a value under key only if the key already exists in keywords.

If key is not present in keywords, it raises a KeyError.

Examples

iex> Keyword.replace!([a: 1, b: 2, a: 3], :a, :new)
[a: :new, b: 2]
iex> Keyword.replace!([a: 1, b: 2, c: 3, b: 4], :b, :new)
[a: 1, b: :new, c: 3]

iex> Keyword.replace!([a: 1], :b, 2)
** (KeyError) key :b not found in: [a: 1]
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replace_lazy(keywords, key, fun)

View Source (since 1.14.0)
@spec replace_lazy(t(), key(), (existing_value :: value() -> new_value :: value())) ::
  t()

Replaces the value under key using the given function only if key already exists in keywords.

In comparison to replace/3, this can be useful when it's expensive to calculate the value.

If key does not exist, the original keyword list is returned unchanged.

Examples

iex> Keyword.replace_lazy([a: 1, b: 2], :a, fn v -> v * 4 end)
[a: 4, b: 2]

iex> Keyword.replace_lazy([a: 2, b: 2, a: 1], :a, fn v -> v * 4 end)
[a: 8, b: 2]

iex> Keyword.replace_lazy([a: 1, b: 2], :c, fn v -> v * 4 end)
[a: 1, b: 2]
@spec split(t(), [key()]) :: {t(), t()}

Takes all entries corresponding to the given keys and extracts them into a separate keyword list.

Returns a tuple with the new list and the old list with removed keys.

Ignores keys for which there are no entries in the keyword list.

Entries with duplicate keys end up in the same keyword list.

Examples

iex> Keyword.split([a: 1, b: 2, c: 3], [:a, :c, :e])
{[a: 1, c: 3], [b: 2]}
iex> Keyword.split([a: 1, b: 2, c: 3, a: 4], [:a, :c, :e])
{[a: 1, c: 3, a: 4], [b: 2]}
Link to this function

split_with(keywords, fun)

View Source (since 1.15.0)
@spec split_with(t(), ({key(), value()} -> as_boolean(term()))) :: {t(), t()}

Splits the keywords into two keyword lists according to the given function fun.

The provided fun receives each {key, value} pair in the keywords as its only argument. Returns a tuple with the first keyword list containing all the elements in keywords for which applying fun returned a truthy value, and a second keyword list with all the elements for which applying fun returned a falsy value (false or nil).

Examples

iex> Keyword.split_with([a: 1, b: 2, c: 3], fn {_k, v} -> rem(v, 2) == 0 end)
{[b: 2], [a: 1, c: 3]}

iex> Keyword.split_with([a: 1, b: 2, c: 3, b: 4], fn {_k, v} -> rem(v, 2) == 0 end)
{[b: 2, b: 4], [a: 1, c: 3]}

iex> Keyword.split_with([a: 1, b: 2, c: 3, b: 4], fn {k, v} -> k in [:a, :c] and rem(v, 2) == 0 end)
{[], [a: 1, b: 2, c: 3, b: 4]}

iex> Keyword.split_with([], fn {_k, v} -> rem(v, 2) == 0 end)
{[], []}
@spec take(t(), [key()]) :: t()

Takes all entries corresponding to the given keys and returns them as a new keyword list.

Preserves duplicate keys in the new keyword list.

Examples

iex> Keyword.take([a: 1, b: 2, c: 3], [:a, :c, :e])
[a: 1, c: 3]
iex> Keyword.take([a: 1, b: 2, c: 3, a: 5], [:a, :c, :e])
[a: 1, c: 3, a: 5]
@spec to_list(t()) :: t()

Returns the keyword list itself.

Examples

iex> Keyword.to_list(a: 1)
[a: 1]
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update(keywords, key, default, fun)

View Source
@spec update(t(), key(), default :: value(), (existing_value :: value() ->
                                          new_value :: value())) :: t()

Updates the value under key in keywords using the given function.

If the key does not exist, it inserts the given default value. Does not pass the default value through the update function.

Removes all duplicate keys and only updates the first one.

Examples

iex> Keyword.update([a: 1], :a, 13, fn existing_value -> existing_value * 2 end)
[a: 2]

iex> Keyword.update([a: 1, a: 2], :a, 13, fn existing_value -> existing_value * 2 end)
[a: 2]

iex> Keyword.update([a: 1], :b, 11, fn existing_value -> existing_value * 2 end)
[a: 1, b: 11]
Link to this function

update!(keywords, key, fun)

View Source
@spec update!(t(), key(), (current_value :: value() -> new_value :: value())) :: t()

Updates the value under key using the given function.

Raises KeyError if the key does not exist.

Removes all duplicate keys and only updates the first one.

Examples

iex> Keyword.update!([a: 1, b: 2, a: 3], :a, &(&1 * 2))
[a: 2, b: 2]
iex> Keyword.update!([a: 1, b: 2, c: 3], :b, &(&1 * 2))
[a: 1, b: 4, c: 3]

iex> Keyword.update!([a: 1], :b, &(&1 * 2))
** (KeyError) key :b not found in: [a: 1]
Link to this function

validate(keyword, values)

View Source (since 1.13.0)
@spec validate(
  keyword(),
  values :: [atom() | {atom(), term()}]
) :: {:ok, keyword()} | {:error, [atom()]}

Ensures the given keyword has only the keys given in values.

The second argument must be a list of atoms, specifying a given key, or tuples specifying a key and a default value.

If the keyword list has only the given keys, it returns {:ok, keyword} with default values applied. Otherwise it returns {:error, invalid_keys} with invalid keys.

See also: validate!/2.

Examples

iex> {:ok, result} = Keyword.validate([], [one: 1, two: 2])
iex> Enum.sort(result)
[one: 1, two: 2]

iex> {:ok, result} = Keyword.validate([two: 3], [one: 1, two: 2])
iex> Enum.sort(result)
[one: 1, two: 3]

If atoms are given, they are supported as keys but do not provide a default value:

iex> {:ok, result} = Keyword.validate([], [:one, two: 2])
iex> Enum.sort(result)
[two: 2]

iex> {:ok, result} = Keyword.validate([one: 1], [:one, two: 2])
iex> Enum.sort(result)
[one: 1, two: 2]

Passing unknown keys returns an error:

iex> Keyword.validate([three: 3, four: 4], [one: 1, two: 2])
{:error, [:four, :three]}

Passing the same key multiple times also errors:

iex> Keyword.validate([one: 1, two: 2, one: 1], [:one, :two])
{:error, [:one]}
Link to this function

validate!(keyword, values)

View Source (since 1.13.0)
@spec validate!(
  keyword(),
  values :: [atom() | {atom(), term()}]
) :: keyword()

Similar to validate/2 but returns the keyword or raises an error.

Examples

iex> Keyword.validate!([], [one: 1, two: 2]) |> Enum.sort()
[one: 1, two: 2]
iex> Keyword.validate!([two: 3], [one: 1, two: 2]) |> Enum.sort()
[one: 1, two: 3]

If atoms are given, they are supported as keys but do not provide a default value:

iex> Keyword.validate!([], [:one, two: 2]) |> Enum.sort()
[two: 2]
iex> Keyword.validate!([one: 1], [:one, two: 2]) |> Enum.sort()
[one: 1, two: 2]

Passing unknown keys raises an error:

iex> Keyword.validate!([three: 3], [one: 1, two: 2])
** (ArgumentError) unknown keys [:three] in [three: 3], the allowed keys are: [:one, :two]

Passing the same key multiple times also errors:

iex> Keyword.validate!([one: 1, two: 2, one: 1], [:one, :two])
** (ArgumentError) duplicate keys [:one] in [one: 1, two: 2, one: 1]
@spec values(t()) :: [value()]

Returns all values from the keyword list.

Keeps values from duplicate keys in the resulting list of values.

Examples

iex> Keyword.values(a: 1, b: 2)
[1, 2]
iex> Keyword.values(a: 1, b: 2, a: 3)
[1, 2, 3]