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implement Map::update #2041

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implement Map::update #2041

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ca23586
implemented Map::update
juliano Apr 29, 2025
f15ad05
Iter::group_by using Map::update
juliano Apr 29, 2025
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1 change: 1 addition & 0 deletions builtin/builtin.mbti
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Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,7 @@ impl Map {
set[K : Hash + Eq, V](Self[K, V], K, V) -> Unit
size[K, V](Self[K, V]) -> Int
to_array[K, V](Self[K, V]) -> Array[(K, V)]
update[K : Hash + Eq, V](Self[K, V], K, (V?) -> V) -> V
values[K, V](Self[K, V]) -> Iter[V]
}
impl[K, V] Default for Map[K, V]
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11 changes: 7 additions & 4 deletions builtin/iter.mbt
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Expand Up @@ -1029,10 +1029,13 @@ pub fn Iter::group_by[T, K : Eq + Hash](
let result = Map::new()
for element in self {
let key = f(element)
match result.get(key) {
Some(arr) => result.set(key, arr + [element])
None => result.set(key, [element])
}
let _ = result.update(key, fn(arr) {
match arr {
Some(existing) => existing + [element]
None => [element]
}
})

}
result
}
53 changes: 53 additions & 0 deletions builtin/linked_hash_map.mbt
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Expand Up @@ -262,6 +262,59 @@ pub fn Map::get_or_init[K : Hash + Eq, V](
}
}

///|
/// Updates the value associated with a key in the map using a function.
///
/// This method applies a function to the current value associated with the key
/// (or `None` if the key does not exist) and sets the key to the result.
///
/// # Parameters
///
/// * `self` - The map to update.
/// * `key` - The key whose value will be updated.
/// * `f` - A function that takes the current value (or `None`) and returns the new value.
///
/// # Returns
///
/// The new value associated with the key after the update.
///
/// # Example
///
/// ```moonbit
/// test "Map::update" {
/// let map = { "a": 1, "b": 2 }
///
/// // Update an existing key
/// let result1 = map.update("a", fn(v) {
/// match v {
/// Some(val) => val * 2
/// None => 0
/// }
/// })
/// assert_eq!(result1, 2)
/// assert_eq!(map.get("a"), Some(2))
///
/// // Update a non-existing key
/// let result2 = map.update("c", fn(v) {
/// match v {
/// Some(val) => val
/// None => 42
/// }
/// })
/// assert_eq!(result2, 42)
/// assert_eq!(map.get("c"), Some(42))
/// }
/// ```
pub fn Map::update[K : Hash + Eq, V](
self : Map[K, V],
key : K,
f : (V?) -> V
) -> V {
let value = f(self.get(key))
self.set(key, value)
value
}

Comment on lines +308 to +317
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The goal was to be efficient, which is not the case with this implementation.

I think you can copy the code of set and modify the line curr_entry.value = value to curr_entry.value = f(Some(value)) and the let entry = { .., value, ..} to let entry = { .., value : f(None), .. }

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Something like this:

  if self.size >= self.growAt {
    self.grow()
  }
  let hash = key.hash()
  let (idx, psl) = for psl = 0, idx = hash & self.capacity_mask {
    match self.entries[idx] {
      None => break (idx, psl)
      Some(curr_entry) => {
        if curr_entry.hash == hash && curr_entry.key == key {
          let new_value = f(Some(value))
          curr_entry.value = new_value
          return new_value
        }
        if psl > curr_entry.psl {
          self.push_away(idx, curr_entry)
          break (idx, psl)
        }
        continue psl + 1, (idx + 1) & self.capacity_mask
      }
    }
  }
  let new_value = f(None)
  let entry = { prev: self.tail, next: None, psl, key, value: new_value, hash }
  self.add_entry_to_tail(idx, entry)
  return new_value

///|
/// Check if the hash map contains a key.
pub fn Map::contains[K : Hash + Eq, V](self : Map[K, V], key : K) -> Bool {
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127 changes: 127 additions & 0 deletions builtin/linked_hash_map_wbtest.mbt
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Expand Up @@ -887,3 +887,130 @@ test "op_equal_key_value_mismatch" {
// This should return false as the values are different
assert_eq!(map1 == map2, false)
}

///|
test "Map::update basic functionality" {
let map = { "a": 1, "b": 2 }
let _ = map.update("a", fn(v) {
match v {
Some(val) => val * 2
None => 0
}
})
assert_eq!(map.get("a"), Some(2))
let _ = map.update("c", fn(v) {
match v {
Some(val) => val
None => 42
}
})
assert_eq!(map.get("c"), Some(42))
}

///|
test "Map::update with complex operations" {
let map = { "counter": 0 }
let _ = map.update("counter", fn(v) {
match v {
Some(val) => val + 1
None => 1
}
})
assert_eq!(map.get("counter"), Some(1))

// Increment again
let _ = map.update("counter", fn(v) {
match v {
Some(val) => val + 1
None => 1
}
})
assert_eq!(map.get("counter"), Some(2))

// Reset counter
let _ = map.update("counter", fn(_) { 0 })
assert_eq!(map.get("counter"), Some(0))
}

///|
test "Map::update with different value types" {
let map : Map[String, Array[Int]] = {}
let res1 = map.update("numbers", fn(v) {
match v {
Some(arr) => {
let new_arr = []
for i in arr {
new_arr.push(i)
}
new_arr.push(1)
new_arr
}
None => [1]
}
})
assert_eq!(res1[0], 1)
assert_eq!(map.get("numbers").unwrap().length(), 1)

// Add more elements
let res2 = map.update("numbers", fn(v) {
match v {
Some(arr) => {
let new_arr = []
for i in arr {
new_arr.push(i)
}
new_arr.push(2)
new_arr.push(3)
new_arr
}
None => [2, 3]
}
})
assert_eq!(res2, [1, 2, 3])
assert_eq!(map.get("numbers").unwrap().length(), 3)
}

///|
test "Map::update with multiple operations" {
let map = {}

// Initialize multiple keys
let _ = map.update("a", fn(_) { 1 })
let _ = map.update("b", fn(_) { 2 })
let _ = map.update("c", fn(_) { 3 })
assert_eq!(map.size(), 3)
assert_eq!(map.get("a"), Some(1))
assert_eq!(map.get("b"), Some(2))
assert_eq!(map.get("c"), Some(3))

// Update all values at once
for k in ["a", "b", "c"] {
let _ = map.update(k, fn(v) {
match v {
Some(val) => val * 10
None => 0
}
})

}
assert_eq!(map.get("a"), Some(10))
assert_eq!(map.get("b"), Some(20))
assert_eq!(map.get("c"), Some(30))
}

///|
test "update preserves order" {
let map = {}

// Add keys in specific order
let _ = map.update("first", fn(_) { 1 })
let _ = map.update("second", fn(_) { 2 })
let _ = map.update("third", fn(_) { 3 })

// Update middle key
let _ = map.update("second", fn(_) { 22 })

// Check that order is preserved
let keys = map.keys().collect()
assert_eq!(keys, ["first", "second", "third"])
}