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hashmap/README.md

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+# Moonbit/Core HashMap
+
+## Overview
+
+A mutable hash map based on a Robin Hood hash table.
+
+## Usage
+
+### Create
+
+You can create an empty map using `new()` or construct it using `from_array()`.
+
+```moonbit
+let map1 : HashMap[String, Int] = HashMap::new()
+let map2 = HashMap::[1, 2, 3, 4, 5]
+```
+
+When creating via `new()`, you can set initial capacity and custom hasher by providing labeled argument `~capacity` and `~hasher`.
+
+```moonbit
+// Create with custom hasher and capacity.
+let map = HashMap::new(~capacity=32, ~hasher=Some(fn(k) { k.length() }))
+```
+
+### Set & Get
+
+You can use `set()` to add a key-value pair to the map, and use `get()` to get a key-value pair.
+
+```moonbit
+let map : HashMap[String, Int] = HashMap::new()
+map.set("a", 1)
+map.get("a") // 1
+```
+
+### Remove
+
+You can use `remove()` to remove a key-value pair.
+
+```moonbit
+let map = HashMap::[("a", 1), ("b", 2), ("c", 3)]
+map.remove("a")
+```
+
+### Contains
+
+You can use `contains()` to check whether a key exists.
+
+```moonbit
+let map = HashMap::[("a", 1), ("b", 2), ("c", 3)]
+map.contains("a") // true
+map.contains("d") // false
+```
+
+### Size & Capacity
+
+You can use `size()` to get the number of key-value pairs in the map, or `capacity()` to get the current capacity.
+
+```moonbit
+let map = HashMap::[("a", 1), ("b", 2), ("c", 3)]
+map.size() // 3
+map.capacity() // 8
+```
+
+Similarly, you can use `is_empty()` to check whether the map is empty.
+
+```moonbit
+let map : HashMap[String, Int] = HashMap::new()
+map.is_empty() // true
+```
+
+### Clear
+
+You can use `clear` to remove all key-value pairs from the map, but the allocated memory will not change.
+
+```moonbit
+let map = HashMap::[("a", 1), ("b", 2), ("c", 3)]
+map.clear()
+map.is_empty() // true
+```
+
+### Iter
+
+You can use `iter()` or `iteri()` to iterate through all key-value pairs.
+
+```moonbit
+let map = HashMap::[("a", 1), ("b", 2), ("c", 3)]
+map.iter(fn(k, v) { println(\(k)-\(v)) })
+map.iteri(fn(i, k, v) { println(\(i)-\(k)-\(v)) })
+```