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(These docs cover all versions between v3 to v8 and are equivalent to the old BuckleScript docs before the rebrand)
Dict
Provide utilities for JS dictionary object.
Note: This module's examples will assume this predeclared dictionary:
RElet ages = Js.Dict.fromList(
[("Maria", 30), ("Vinh", 22), ("Fred", 49)]
);
t
REtype t('a);
Dictionary type (ie an '' JS object). However it is restricted to hold a single type; therefore values must have the same type. This Dictionary type is mostly used with the Js_json.t type.
key
REtype key = string;
The type for dictionary keys. This means that dictionaries must use string
s as their keys.
get
RElet get: (t('a), key) => option('a);
Js.Dict.get(key)
returns None
if the key is not found in the dictionary, Some(value)
otherwise.
REJs.Dict.get(ages, "Vinh") == Some(22);
Js.Dict.get(ages, "Paul") == None;
unsafeGet
RElet unsafeGet: (t('a), key) => 'a;
Js.Dict.unsafeGet(key)
returns the value if the key exists, otherwise an undefined
value is returned. Use this only when you are sure the key exists (i.e. when having used the keys()
function to check that the key is valid).
REJs.Dict.unsafeGet(ages, "Fred") == 49;
Js.Dict.unsafeGet(ages, "Paul"); // returns undefined
set
RElet set: (t('a), key, 'a) => unit;
Js.Dict.set(dict, key, value)
sets the key/value in the dictionary dict
. If the key does not exist, and entry will be created for it. This function modifies the original dictionary.
REJs.Dict.set(ages, "Maria", 31)
Js.log(ages ==
Js.Dict.fromList([("Maria", 31), ("Vinh", 22), ("Fred", 49)]));
Js.Dict.set(ages, "David", 66)
Js.log(ages ==
Js.Dict.fromList([("Maria", 31), ("Vinh", 22), ("Fred", 49), ("David", 66)]));
keys
RElet keys: t('a) => array(string);
Returns all the keys in the dictionary dict
.
REJs.Dict.keys(ages) == [|"Maria", "Vinh", "Fred"|];
empty
RElet empty: unit => t('a);
Returns an empty dictionary.
unsafeDeleteKey
RElet unsafeDeleteKey: (. t(string), string) => unit;
Experimental internal function
entries
RElet entries: t('a) => array((key, 'a));
Returns an array of key/value pairs in the given dictionary (ES2017).
REJs.Dict.entries(ages) == [|("Maria", 30), ("Vinh", 22), ("Fred", 49)|]
values
RElet values: t('a) => array('a);
Returns the values in the given dictionary (ES2017).
REJs.Dict.values(ages) == [|30, 22, 49|]
fromList
RElet fromList: list((key, 'a)) => t('a);
Creates a new dictionary containing each (key, value) pair in its list argument.
RElet capitals = Js.Dict.fromList([("Japan", "Tokyo"), ("France", "Paris"), ("Egypt", "Cairo")]);
fromArray
RElet fromArray: array((key, 'a)) => t('a);
Creates a new dictionary containing each (key, value) pair in its array argument.
RElet capitals2 = Js.Dict.fromArray([|("Germany", "Berlin"), ("Burkina Faso", "Ouagadougou")|]);
map
RElet map: ((. 'a) => 'b, t('a)) => t('b);
map(f, dict)
maps dict
to a new dictionary with the same keys, using the function f
to map each value.
RElet prices = Js.Dict.fromList([("pen", 1.00), ("book", 5.00), ("stapler", 7.00)]);
let discount = (. price) => {price *. 0.90};
let salePrices = Js.Dict.map(discount, prices);
salePrices == Js.Dict.fromList([("pen", 0.90), ("book", 4.50), ("stapler", 6.30)]);