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Add getWithDefault and getOrThrow to Belt.HashMap
Belt.HashMap, Belt.HashMap.Int and Belt.HashMap.String gain getWithDefault and getOrThrow, the same lookups Belt.Map and Belt.MutableMap already have. They walk the bucket directly, so a hit allocates no option; getOrThrow throws Not_found like the other Belt maps. Example (rescript): let m = Belt.HashMap.Int.fromArray([(1, "a")]) m->Belt.HashMap.Int.getWithDefault(2, "z") == "z" m->Belt.HashMap.Int.getOrThrow(1) == "a" Review: Why getWithDefault and not getOr, as the issue title says? Belt names this lookup getWithDefault everywhere (Option, Map, MutableMap and their Int/String variants) and has no getOr; the new functions follow Belt. getOrThrow is the name Belt already uses, without a deprecated getExn alias for a new API. Area: runtime tests Output: changed tests/belt_tests/src/belt_hashmap_test.mjs (new tests); no existing program compiles differently Tests: ~tests/belt_tests/src/belt_hashmap_test.res plus docstring examples in Belt_HashMap.resi, Belt_HashMapInt.resi, Belt_HashMapString.resi Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kr4cjoUi2f5VpMvE6wT9bo Signed-off-by: Christoph Knittel <ck@cca.io>
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‎changes/belt-hashmap-get-with-default.feature.md‎

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- Add `getWithDefault` and `getOrThrow` to `Belt.HashMap`, `Belt.HashMap.Int` and `Belt.HashMap.String`.

‎packages/@rescript/belt/src/Belt_HashMap.res‎

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@@ -170,6 +170,40 @@ let get = (h, key) => {
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}
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}
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let rec getWithDefaultAux = (~eq, key, buckets, default) =>
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switch C.toOpt(buckets) {
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| None => default
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| Some(cell) =>
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if eq(key, cell.N.key) {
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cell.N.value
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} else {
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getWithDefaultAux(~eq, key, cell.N.next, default)
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}
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}
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let getWithDefault = (h, key, default) => {
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let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(Belt_Id.getHashInternal(h.C.hash)(key), A.length(h_buckets) - 1)
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getWithDefaultAux(~eq=Belt_Id.getEqInternal(h.C.eq), key, A.getUnsafe(h_buckets, nid), default)
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}
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let rec getOrThrowAux = (~eq, key, buckets) =>
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switch C.toOpt(buckets) {
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| None => throw(Not_found)
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| Some(cell) =>
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if eq(key, cell.N.key) {
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cell.N.value
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} else {
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getOrThrowAux(~eq, key, cell.N.next)
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}
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}
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let getOrThrow = (h, key) => {
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let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(Belt_Id.getHashInternal(h.C.hash)(key), A.length(h_buckets) - 1)
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getOrThrowAux(~eq=Belt_Id.getEqInternal(h.C.eq), key, A.getUnsafe(h_buckets, nid))
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}
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let rec memInBucket = (key, cell, ~eq) =>
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eq(cell.N.key, key) ||
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switch C.toOpt(cell.N.next) {

‎packages/@rescript/belt/src/Belt_HashMap.resi‎

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@@ -203,6 +203,52 @@ Belt.HashMap.has(s0, 2) == false
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*/
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let has: (t<'key, 'value, 'id>, 'key) => bool
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/**
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`getWithDefault(tbl, k, default)` returns the value bound to `k`, or `default` if `k` is not bound.
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## Examples
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```rescript
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module IntHash = Belt.Id.MakeHashable({
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type t = int
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let hash = a => a
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let eq = (a, b) => a == b
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})
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let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
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Belt.HashMap.set(s0, 1, "value1")
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Belt.HashMap.getWithDefault(s0, 1, "default") == "value1"
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Belt.HashMap.getWithDefault(s0, 2, "default") == "default"
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```
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*/
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let getWithDefault: (t<'key, 'value, 'id>, 'key, 'value) => 'value
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/**
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`getOrThrow(tbl, k)` returns the value bound to `k`. Throws `Not_found` if `k` is not bound.
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## Examples
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```rescript
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module IntHash = Belt.Id.MakeHashable({
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type t = int
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let hash = a => a
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let eq = (a, b) => a == b
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})
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let s0 = Belt.HashMap.make(~hintSize=10, ~id=module(IntHash))
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Belt.HashMap.set(s0, 1, "value1")
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Belt.HashMap.getOrThrow(s0, 1) == "value1"
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switch Belt.HashMap.getOrThrow(s0, 2) {
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| exception Not_found => assert(true)
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| _ => assert(false)
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}
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```
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*/
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let getOrThrow: (t<'key, 'value, 'id>, 'key) => 'value
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/**
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If bound exists, removes it from the hash map.
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‎packages/@rescript/belt/src/Belt_HashMapInt.res‎

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@@ -154,6 +154,40 @@ let get = (h, key: key) => {
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}
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}
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let rec getWithDefaultAux = (key: key, buckets, default) =>
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switch C.toOpt(buckets) {
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| None => default
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| Some(cell) =>
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if key == cell.N.key {
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cell.N.value
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} else {
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getWithDefaultAux(key, cell.N.next, default)
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}
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}
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let getWithDefault = (h, key: key, default) => {
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let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(hash(key), A.length(h_buckets) - 1)
171+
getWithDefaultAux(key, A.getUnsafe(h_buckets, nid), default)
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}
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let rec getOrThrowAux = (key: key, buckets) =>
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switch C.toOpt(buckets) {
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| None => throw(Not_found)
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| Some(cell) =>
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if key == cell.N.key {
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cell.N.value
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} else {
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getOrThrowAux(key, cell.N.next)
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}
183+
}
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let getOrThrow = (h, key: key) => {
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let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(hash(key), A.length(h_buckets) - 1)
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getOrThrowAux(key, A.getUnsafe(h_buckets, nid))
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}
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let rec memInBucket = (key: key, cell) =>
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cell.N.key == key ||
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switch C.toOpt(cell.next) {

‎packages/@rescript/belt/src/Belt_HashMapInt.resi‎

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@@ -19,6 +19,38 @@ let get: (t<'a>, key) => option<'a>
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2020
let has: (t<'b>, key) => bool
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/**
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`getWithDefault(tbl, k, default)` returns the value bound to `k`, or `default` if `k` is not bound.
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## Examples
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```rescript
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let hMap = Belt.HashMap.Int.fromArray([(1, "value1")])
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Belt.HashMap.Int.getWithDefault(hMap, 1, "default") == "value1"
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Belt.HashMap.Int.getWithDefault(hMap, 2, "default") == "default"
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```
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*/
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let getWithDefault: (t<'a>, key, 'a) => 'a
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/**
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`getOrThrow(tbl, k)` returns the value bound to `k`. Throws `Not_found` if `k` is not bound.
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## Examples
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```rescript
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let hMap = Belt.HashMap.Int.fromArray([(1, "value1")])
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Belt.HashMap.Int.getOrThrow(hMap, 1) == "value1"
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switch Belt.HashMap.Int.getOrThrow(hMap, 2) {
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| exception Not_found => assert(true)
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| _ => assert(false)
49+
}
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```
51+
*/
52+
let getOrThrow: (t<'a>, key) => 'a
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2254
let remove: (t<'a>, key) => unit
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@deprecated("Use `forEach` instead")

‎packages/@rescript/belt/src/Belt_HashMapString.res‎

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@@ -154,6 +154,40 @@ let get = (h, key: key) => {
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}
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}
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let rec getWithDefaultAux = (key: key, buckets, default) =>
158+
switch C.toOpt(buckets) {
159+
| None => default
160+
| Some(cell) =>
161+
if key == cell.N.key {
162+
cell.N.value
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} else {
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getWithDefaultAux(key, cell.N.next, default)
165+
}
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}
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let getWithDefault = (h, key: key, default) => {
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let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(hash(key), A.length(h_buckets) - 1)
171+
getWithDefaultAux(key, A.getUnsafe(h_buckets, nid), default)
172+
}
173+
174+
let rec getOrThrowAux = (key: key, buckets) =>
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switch C.toOpt(buckets) {
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| None => throw(Not_found)
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| Some(cell) =>
178+
if key == cell.N.key {
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cell.N.value
180+
} else {
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getOrThrowAux(key, cell.N.next)
182+
}
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}
184+
185+
let getOrThrow = (h, key: key) => {
186+
let h_buckets = h.C.buckets
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let nid = Int.bitwiseAnd(hash(key), A.length(h_buckets) - 1)
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getOrThrowAux(key, A.getUnsafe(h_buckets, nid))
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}
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let rec memInBucket = (key: key, cell) =>
158192
cell.N.key == key ||
159193
switch C.toOpt(cell.next) {

‎packages/@rescript/belt/src/Belt_HashMapString.resi‎

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Original file line numberDiff line numberDiff line change
@@ -19,6 +19,38 @@ let get: (t<'a>, key) => option<'a>
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2020
let has: (t<'b>, key) => bool
2121

22+
/**
23+
`getWithDefault(tbl, k, default)` returns the value bound to `k`, or `default` if `k` is not bound.
24+
25+
## Examples
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27+
```rescript
28+
let hMap = Belt.HashMap.String.fromArray([("a", "value1")])
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30+
Belt.HashMap.String.getWithDefault(hMap, "a", "default") == "value1"
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Belt.HashMap.String.getWithDefault(hMap, "b", "default") == "default"
32+
```
33+
*/
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let getWithDefault: (t<'a>, key, 'a) => 'a
35+
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/**
37+
`getOrThrow(tbl, k)` returns the value bound to `k`. Throws `Not_found` if `k` is not bound.
38+
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## Examples
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```rescript
42+
let hMap = Belt.HashMap.String.fromArray([("a", "value1")])
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44+
Belt.HashMap.String.getOrThrow(hMap, "a") == "value1"
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switch Belt.HashMap.String.getOrThrow(hMap, "b") {
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| exception Not_found => assert(true)
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| _ => assert(false)
49+
}
50+
```
51+
*/
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let getOrThrow: (t<'a>, key) => 'a
53+
2254
let remove: (t<'a>, key) => unit
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2456
@deprecated("Use `forEach` instead")

‎tests/belt_tests/src/belt_hashmap_test.mjs‎

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Original file line numberDiff line numberDiff line change
@@ -9,6 +9,8 @@ import * as Belt_HashMap from "@rescript/belt/src/Belt_HashMap.mjs";
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import * as Primitive_int from "@rescript/runtime/lib/es6/Primitive_int.mjs";
1010
import * as Belt_SortArray from "@rescript/belt/src/Belt_SortArray.mjs";
1111
import * as Array_data_util from "./array_data_util.mjs";
12+
import * as Belt_HashMapInt from "@rescript/belt/src/Belt_HashMapInt.mjs";
13+
import * as Belt_HashMapString from "@rescript/belt/src/Belt_HashMapString.mjs";
1214

1315
function intEq(x, y) {
1416
return x === y;
@@ -67,6 +69,71 @@ Mocha.describe("Belt_hashmap_test", () => {
6769
Test_utils.eq("File \"belt_hashmap_test.res\", line 43, characters 7-14", Belt_HashMap.size(v), 98000);
6870
Test_utils.ok("File \"belt_hashmap_test.res\", line 44, characters 7-14", Belt_Array.every(Array_data_util.range(2001, 100000), x => Belt_HashMap.has(v, x)));
6971
});
72+
Mocha.test("getWithDefault and getOrThrow", () => {
73+
let v = Belt_HashMap.fromArray([
74+
[
75+
1,
76+
10
77+
],
78+
[
79+
2,
80+
20
81+
]
82+
], Y);
83+
Test_utils.eq("File \"belt_hashmap_test.res\", line 49, characters 7-14", Belt_HashMap.getWithDefault(v, 1, 0), 10);
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Test_utils.eq("File \"belt_hashmap_test.res\", line 50, characters 7-14", Belt_HashMap.getWithDefault(v, 3, 0), 0);
85+
Test_utils.eq("File \"belt_hashmap_test.res\", line 51, characters 7-14", Belt_HashMap.getOrThrow(v, 2), 20);
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Test_utils.throws("File \"belt_hashmap_test.res\", line 52, characters 11-18", () => {
87+
Belt_HashMap.getOrThrow(v, 3);
88+
});
89+
});
90+
Mocha.test("getWithDefault and getOrThrow with colliding keys", () => {
91+
let Collide = Belt_Id.hashable(param => 0, intEq);
92+
let v = Belt_HashMap.make(4, Collide);
93+
for (let i = 0; i <= 9; ++i) {
94+
Belt_HashMap.set(v, i, i * 10 | 0);
95+
}
96+
Test_utils.ok("File \"belt_hashmap_test.res\", line 61, characters 7-14", Belt_Array.every(Array_data_util.range(0, 9), i => Belt_HashMap.getWithDefault(v, i, -1) === (i * 10 | 0)));
97+
Test_utils.ok("File \"belt_hashmap_test.res\", line 62, characters 7-14", Belt_Array.every(Array_data_util.range(0, 9), i => Belt_HashMap.getOrThrow(v, i) === (i * 10 | 0)));
98+
Test_utils.eq("File \"belt_hashmap_test.res\", line 63, characters 7-14", Belt_HashMap.getWithDefault(v, 10, -1), -1);
99+
Test_utils.throws("File \"belt_hashmap_test.res\", line 64, characters 11-18", () => {
100+
Belt_HashMap.getOrThrow(v, 10);
101+
});
102+
});
103+
Mocha.test("Int and String getWithDefault and getOrThrow", () => {
104+
let i = Belt_HashMapInt.fromArray([
105+
[
106+
1,
107+
"a"
108+
],
109+
[
110+
2,
111+
"b"
112+
]
113+
]);
114+
Test_utils.eq("File \"belt_hashmap_test.res\", line 69, characters 7-14", Belt_HashMapInt.getWithDefault(i, 2, "z"), "b");
115+
Test_utils.eq("File \"belt_hashmap_test.res\", line 70, characters 7-14", Belt_HashMapInt.getWithDefault(i, 3, "z"), "z");
116+
Test_utils.eq("File \"belt_hashmap_test.res\", line 71, characters 7-14", Belt_HashMapInt.getOrThrow(i, 1), "a");
117+
Test_utils.throws("File \"belt_hashmap_test.res\", line 72, characters 11-18", () => {
118+
Belt_HashMapInt.getOrThrow(i, 3);
119+
});
120+
let s = Belt_HashMapString.fromArray([
121+
[
122+
"a",
123+
1
124+
],
125+
[
126+
"b",
127+
2
128+
]
129+
]);
130+
Test_utils.eq("File \"belt_hashmap_test.res\", line 74, characters 7-14", Belt_HashMapString.getWithDefault(s, "b", 0), 2);
131+
Test_utils.eq("File \"belt_hashmap_test.res\", line 75, characters 7-14", Belt_HashMapString.getWithDefault(s, "c", 0), 0);
132+
Test_utils.eq("File \"belt_hashmap_test.res\", line 76, characters 7-14", Belt_HashMapString.getOrThrow(s, "a"), 1);
133+
Test_utils.throws("File \"belt_hashmap_test.res\", line 77, characters 11-18", () => {
134+
Belt_HashMapString.getOrThrow(s, "c");
135+
});
136+
});
70137
});
71138

72139
let N;

‎tests/belt_tests/src/belt_hashmap_test.res‎

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Original file line numberDiff line numberDiff line change
@@ -43,4 +43,37 @@ describe(__MODULE__, () => {
4343
eq(__LOC__, N.size(v), 98_000)
4444
ok(__LOC__, A.every(I.range(2_001, 100_000), x => N.has(v, x)))
4545
})
46+
47+
test("getWithDefault and getOrThrow", () => {
48+
let v = N.fromArray(~id=module(Y), [(1, 10), (2, 20)])
49+
eq(__LOC__, N.getWithDefault(v, 1, 0), 10)
50+
eq(__LOC__, N.getWithDefault(v, 3, 0), 0)
51+
eq(__LOC__, N.getOrThrow(v, 2), 20)
52+
throws(__LOC__, () => N.getOrThrow(v, 3)->ignore)
53+
})
54+
55+
test("getWithDefault and getOrThrow with colliding keys", () => {
56+
module Collide = unpack(Belt.Id.hashable(~eq=intEq, ~hash=(_: int) => 0))
57+
let v = N.make(~id=module(Collide), ~hintSize=4)
58+
for i in 0 to 9 {
59+
N.set(v, i, i * 10)
60+
}
61+
ok(__LOC__, A.every(I.range(0, 9), i => N.getWithDefault(v, i, -1) == i * 10))
62+
ok(__LOC__, A.every(I.range(0, 9), i => N.getOrThrow(v, i) == i * 10))
63+
eq(__LOC__, N.getWithDefault(v, 10, -1), -1)
64+
throws(__LOC__, () => N.getOrThrow(v, 10)->ignore)
65+
})
66+
67+
test("Int and String getWithDefault and getOrThrow", () => {
68+
let i = Belt.HashMap.Int.fromArray([(1, "a"), (2, "b")])
69+
eq(__LOC__, Belt.HashMap.Int.getWithDefault(i, 2, "z"), "b")
70+
eq(__LOC__, Belt.HashMap.Int.getWithDefault(i, 3, "z"), "z")
71+
eq(__LOC__, Belt.HashMap.Int.getOrThrow(i, 1), "a")
72+
throws(__LOC__, () => Belt.HashMap.Int.getOrThrow(i, 3)->ignore)
73+
let s = Belt.HashMap.String.fromArray([("a", 1), ("b", 2)])
74+
eq(__LOC__, Belt.HashMap.String.getWithDefault(s, "b", 0), 2)
75+
eq(__LOC__, Belt.HashMap.String.getWithDefault(s, "c", 0), 0)
76+
eq(__LOC__, Belt.HashMap.String.getOrThrow(s, "a"), 1)
77+
throws(__LOC__, () => Belt.HashMap.String.getOrThrow(s, "c")->ignore)
78+
})
4679
})

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