diff --git a/std/arraylist/arraylist.test.bro b/std/arraylist/arraylist.test.bro
index 8a9393a..ae64e8d 100644
--- a/std/arraylist/arraylist.test.bro
+++ b/std/arraylist/arraylist.test.bro
@@ -7,7 +7,6 @@ handles_append test {
 
 	try append(&list, 42)
 
-	try testing.expect_type(usize, list.items.len)
 	try testing.expect_equal(1, list.items.len)
 	try testing.expect_equal(42, list.items[0])
 }
diff --git a/std/build/build.bro b/std/build/build.bro
index cf2f884..8e48122 100644
--- a/std/build/build.bro
+++ b/std/build/build.bro
@@ -7,11 +7,11 @@
 # Declarative and literal-only: one executable per build. List fields take an
 # address-of an array literal (`&["raylib"]`) and default to empty.
 BuildConfig :: struct {
-	name      []u8      # output executable name under root/build
-	source    []u8      # program package directory, relative to build.bro
+	name []u8              # output executable name under root/build
+	source []u8            # program package directory, relative to build.bro
 	libraries [][]u8 = &[] # library names to link (-l)
 	lib_paths [][]u8 = &[] # library search directories (-L)
-	includes  [][]u8 = &[] # C include directories (-I)
-	defines   [][]u8 = &[] # C preprocessor defines (name or name=value)
-	links     [][]u8 = &[] # extra linker inputs (object/source files, -framework pairs)
+	includes [][]u8 = &[]  # C include directories (-I)
+	defines [][]u8 = &[]   # C preprocessor defines (name or name=value)
+	links [][]u8 = &[]     # extra linker inputs (object/source files, -framework pairs)
 }
diff --git a/std/enums/enums.bro b/std/enums/enums.bro
new file mode 100644
index 0000000..d6a2624
--- /dev/null
+++ b/std/enums/enums.bro
@@ -0,0 +1,45 @@
+import "@std/meta"
+
+EnumMap func($E, $V type) type {
+    match typeinfo!(E) {
+        .enum |info|: return struct {
+	        present [info.fields.len]mut bool # fixme: replace with bitset
+	       	values [info.fields.len]mut V
+        }
+        else: compile_error!("EnumMap key must be an enum")
+    }
+}
+
+init func(
+	$E, $V type,
+	values meta.EnumFieldStruct(E, ?V, some!(null)),
+) EnumMap(E, V) {
+	map EnumMap(E, V) = undefined
+
+	match typeinfo!(E) {
+		.enum |info|: expand for info.fields |field, i| {
+			map.present[i] = false
+
+			if field!(values, field.name) |value| {
+				map.present[i] = true
+				map.values[i] = value
+			}
+		}
+		else: compile_error!("EnumMap key must be an enum")
+	}
+
+	return map
+}
+
+get func($E, $V type, map @EnumMap(E, V), key E) ?V {
+	# fixme: linear lookup; implement an enum index/discriminant map for O(1) lookup
+	match typeinfo!(E) {
+		.enum |info|: expand for info.fields |field, i| {
+			if key == field!(E, field.name) {
+				if (map.present[i]) return map.values[i]
+				return null
+			}
+		}
+		else: compile_error!("EnumMap key must be an enum")
+	}
+}
diff --git a/std/enums/enums.test.bro b/std/enums/enums.test.bro
new file mode 100644
index 0000000..d50441a
--- /dev/null
+++ b/std/enums/enums.test.bro
@@ -0,0 +1,25 @@
+import "@std/mem"
+import "@std/testing"
+
+TestEnum :: enum(u8) {
+	ident = 3
+	int = 8
+	eof = 21
+}
+
+handles_sparse_enum_get test {
+	names EnumMap(TestEnum, []u8) = init({
+		ident = "identifier",
+		int = "integer",
+	})
+
+	ident :: get(&names, TestEnum.ident)
+
+	try testing.expect_type(?[]u8, ident)
+	try testing.expect(mem.eql("identifier", ident?))
+
+	eof :: get(&names, TestEnum.eof)
+
+	try testing.expect_type(?[]u8, eof)
+	try testing.expect_equal(null, eof)
+}
diff --git a/std/hashmap/hashmap.bro b/std/hashmap/hashmap.bro
new file mode 100644
index 0000000..6141049
--- /dev/null
+++ b/std/hashmap/hashmap.bro
@@ -0,0 +1,160 @@
+import "@std/mem"
+
+PutError :: enum { key_exists }
+
+Entry func($K, $V type) type {
+	return struct {
+		# hash = 0 means empty
+		hash usize = 0
+		key K
+		value V
+	}
+}
+
+HashMap func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+) type {
+	return struct {
+		entries []mut Entry(K, V)
+		count usize
+		allocator mem.Allocator
+	}
+}
+
+StringHashMap func($V type) type {
+	return HashMap([]u8, V, str_hash, str_eql)
+}
+
+init func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	allocator mem.Allocator,
+) HashMap(K, V, hash_key, keys_eql) {
+	return HashMap(K, V, hash_key, keys_eql){
+		entries = mem.empty(Entry(K, V)),
+		count = 0,
+		allocator = allocator,
+	}
+}
+
+# free the entries in the hash map.
+# note: this operation invalidates the map.
+deinit func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @HashMap(K, V, hash_key, keys_eql),
+) void { mem.free(map.allocator, map.entries) }
+
+get func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @HashMap(K, V, hash_key, keys_eql),
+	key K,
+) ?V {
+	if (map.count == 0) return null
+
+	hash :: normalize(hash_key(key))
+	idx usize = hash & (map.entries.len - 1)
+
+	while true {
+		entry :: map.entries[idx]
+		if (entry.hash == 0) return null
+
+		if (entry.hash == hash and keys_eql(entry.key, key)) {
+			return entry.value
+		}
+
+		idx = (idx + 1) & (map.entries.len - 1)
+	}
+}
+
+put func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @mut HashMap(K, V, hash_key, keys_eql),
+	key K,
+	value V,
+) void ! (PutError | mem.AllocError) {
+	# check grow
+	threshold :: map.entries.len - divtrunc!(map.entries.len, 4)
+	if (map.entries.len == 0 or map.count + 1 > threshold) {
+		old_entries :: map.entries
+		new_size :: if (old_entries.len > 0) old_entries.len * 2 else 8
+		new_entries :: try mem.alloc(Entry(K, V), map.allocator, new_size)
+
+		# zero new entries
+		for 0..new_entries.len |i| {
+			new_entries[i].hash = 0
+		}
+
+		# move old entries
+		for old_entries |entry| {
+			if (entry.hash == 0) continue
+
+			# find an empty slot
+			idx usize = entry.hash & (new_entries.len - 1)
+			while new_entries[idx].hash != 0 {
+				idx = (idx + 1) & (new_entries.len - 1)
+			}
+
+			new_entries[idx] = entry
+		}
+
+		map.entries = new_entries
+		mem.free(map.allocator, old_entries)
+	}
+
+	# put new entry
+	hash :: normalize(hash_key(key))
+	idx usize = hash & (map.entries.len - 1)
+
+	while true {
+		entry :: map.entries[idx]
+		if entry.hash == 0 {
+			map.entries[idx] = Entry(K, V){
+				hash = hash,
+				key = key,
+				value = value,
+			}
+			map.count += 1
+			return
+		}
+
+		if (entry.hash == hash and keys_eql(entry.key, key)) {
+			return .key_exists
+		}
+
+		idx = (idx + 1) & (map.entries.len - 1)
+	}
+}
+
+hide normalize func(hash usize) usize {
+	# mapping both 0 and 1 to 1 is safe because equality resolves
+	# collisions (since hash and key must both be equal).
+	if (hash == 0) return 1
+	return hash
+}
+
+#! FNV-1a hash implementation.
+#! note: vulnerable to collision attacks.
+hide str_hash func(key []u8) usize {
+	hash u32 = 2166136261 # offset basis
+	prime u32 = 16777619
+
+	for key |byte| {
+		product u64 :: u64(hash xor u32(byte)) * prime
+		hash = u32(product & u64(maxval!(u32)))
+	}
+
+	return usize(hash)
+}
+
+hide str_eql func(a, b []u8) bool {
+	return mem.eql(a, b)
+}
diff --git a/std/hashmap/hashmap.test.bro b/std/hashmap/hashmap.test.bro
new file mode 100644
index 0000000..57ff8a4
--- /dev/null
+++ b/std/hashmap/hashmap.test.bro
@@ -0,0 +1,13 @@
+import "@std/mem"
+import "@std/testing"
+
+handles_put_and_get test {
+	map StringHashMap(u32) = init(mem.c_allocator)
+	defer deinit(&map)
+
+	try put(&map, "key", 42)
+	value :: get(&map, "key")
+
+	try testing.expect_type(?u32, value)
+	try testing.expect_equal(42, value?)
+}
diff --git a/std/mem/mem.bro b/std/mem/mem.bro
index 1807bf8..1484a8f 100644
--- a/std/mem/mem.bro
+++ b/std/mem/mem.bro
@@ -41,17 +41,7 @@ eql func($T type, left, right []T) bool {
 	return true
 }
 
-hide empty_storage [1]mut u64 = [0]
-
-hide empty_slice func($T type, count usize) []mut T {
-	pointer *mut T :: ptrcast!(T, (&empty_storage).ptr)
-	return pointer[..count]
-}
-
-empty func($T type) []mut T {
-	return empty_slice(T, 0)
-}
-
+# allocate memory for a slice of type `T` with `count` elements.
 alloc func($T type, allocator Allocator, count usize) []mut T ! AllocError {
 	if count == 0 {
 		return empty_slice(T, 0)
@@ -73,10 +63,14 @@ alloc func($T type, allocator Allocator, count usize) []mut T ! AllocError {
 	return .out_of_memory
 }
 
+# reallocate memory for a slice of type `T` with `new_count` elements.
+# reallocating with `new_count == 0` will free the memory and return an empty slice.
+# note: memory must be reallocated with the same allocator that was used to allocate it.
 realloc func($T type, allocator Allocator, memory []mut T, new_count usize) []mut T ! AllocError {
 	if new_count == memory.len {
 		return memory
 	}
+
 	if new_count == 0 {
 		free(allocator, memory)
 		return empty_slice(T, 0)
@@ -107,9 +101,12 @@ realloc func($T type, allocator Allocator, memory []mut T, new_count usize) []mu
 		pointer *mut T :: ptrcast!(T, bytes)
 		return pointer[..new_count]
 	}
+
 	return .out_of_memory
 }
 
+# free memory allocated for a slice of type `T`.
+# note: memory must be freed with the same allocator that was used to allocate it.
 free func($T type, allocator Allocator, memory []T) void {
 	if memory.len != 0 and sizeof!(T) != 0 {
 		mutable_memory []mut T :: constcast!(memory)
@@ -117,6 +114,19 @@ free func($T type, allocator Allocator, memory []T) void {
 	}
 }
 
+# get an empty slice of type `T` with `count` elements.
+empty_slice func($T type, count usize) []mut T {
+	pointer *mut T :: ptrcast!(T, (&empty_storage).ptr)
+	return pointer[..count]
+}
+
+# get an empty slice of type `T` with 0 elements.
+empty func($T type) []mut T {
+	return empty_slice(T, 0)
+}
+
+hide empty_storage [1]mut u64 = [0]
+
 hide malloc_alignment usize :: 16 # ponytail: aarch64-macos libc malloc alignment assumption.
 
 hide power_of_two func(value usize) bool {
diff --git a/std/meta/meta.bro b/std/meta/meta.bro
index e9b0dc0..5780e89 100644
--- a/std/meta/meta.bro
+++ b/std/meta/meta.bro
@@ -44,9 +44,9 @@ TypeInfo :: union(enum) {
 EnumFieldStruct func($E, $Field type, $default ?Field) type {
 	match typeinfo!(E) {
 		.enum |info|: {
-			names [info.fields.len]mut []u8 = undefined
-			field_types [info.fields.len]mut type = undefined
-			defaults [info.fields.len]mut ?Field = undefined
+		names [info.fields.len]mut []u8 = undefined
+		field_types [info.fields.len]mut type = undefined
+		defaults [info.fields.len]mut ?Field = undefined
 			expand for info.fields |field, index| {
 				names[index] = field.name
 				field_types[index] = Field
diff --git a/std/std.bro b/std/std.bro
index d4697ad..0da939b 100644
--- a/std/std.bro
+++ b/std/std.bro
@@ -1,5 +1,7 @@
 import "io"
+import "enums"
 import "arraylist"
 
 Io :: alias io.Io
 ArrayList :: alias arraylist.ArrayList
+EnumMap :: alias enums.EnumMap
diff --git a/std/testing/testing.bro b/std/testing/testing.bro
index e5e08c0..964dab3 100644
--- a/std/testing/testing.bro
+++ b/std/testing/testing.bro
@@ -38,9 +38,11 @@ expect_equal func($T type, expected, actual T, location SourceLocation) void ! E
 			debug.print("{s}:{d}:{d}: expected and actual slices differ\n", {location.file, location.line, location.column})
 			return .expectation_failed
 		}
-		else: if expected != actual {
-			debug.print("{s}:{d}:{d}: expected {}, found {}\n", {location.file, location.line, location.column, expected, actual})
-			return .expectation_failed
+		else: {
+			if expected != actual {
+				debug.print("{s}:{d}:{d}: expected {}, found {}\n", {location.file, location.line, location.column, expected, actual})
+				return .expectation_failed
+			}
 		}
 	}
 }