diff --git a/cig.h b/cig.h
index cf801f4..3ae9417 100644
--- a/cig.h
+++ b/cig.h
@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdbool.h>
+#include <string.h>
 
 typedef union any_align { char c; int i; long l; long long ll; float f; double d; void *p; long double ld; } any_align_t;
 #define MAX_ALIGN ((size_t) sizeof(any_align_t))
@@ -106,9 +107,13 @@ allocator_t allocator_from_arena(arena_allocator_t *this);
 // dynamic arrays //////////////////////////////////////////////////////////////
 
 typedef struct dyn_array_header {
-	size_t size, capacity, itemsize;
+	size_t n_items, capacity, itemsize;
 	allocator_t allocator;
-	uint8_t bytes[];
+	union {
+		// allocates a little more memory than needed, but who cares?
+		uint8_t bytes[1];
+		any_align_t _[1];
+	};
 } dyn_array_header_t;
 
 typedef struct dyn_array_create_func_args {
@@ -142,7 +147,7 @@ void dyn_array_shrink_func(void *this, size_t n_items_to_remove, const char *fil
 #define arr_reset(THIS)\
   do {\
 	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, THIS);\
-	header->size = 0;\
+	header->n_items = 0;\
   } while (0)
 
 size_t arr_len(void *this);
@@ -156,6 +161,28 @@ size_t arr_cap(void *this);
 
 #define arr_pop(THIS) (arr_shrink(THIS, 1), THIS[arr_len(THIS)])
 
+
+/* Compile-time assert that works in expression contexts */
+#define STATIC_ASSERT(expr) ((void)sizeof(char[(expr) ? 1 : -1]))
+
+
+bool dyn_array_contains_func(void *this, uint8_t *value);
+
+/*
+    arr_contains(THIS, TYPE, VALUE)
+
+    - SIZE CHECK: compile-time check that sizeof(*THIS) == sizeof(TYPE)
+    - TYPE is the type of the value to search for
+    - VALUE is stored in a compound literal of TYPE
+    - Pure C99, no extensions needed
+    - Callers with typeof support can make wrapper macros
+*/
+#define arr_contains(THIS, TYPE, VALUE)\
+    (\
+        STATIC_ASSERT(sizeof(*(THIS)) == sizeof(TYPE)),\
+        dyn_array_contains_func((THIS), (uint8_t*)&(TYPE){(VALUE)})\
+    )
+
 // CLI /////////////////////////////////////////////////////////////////////////
 
 #define CLI_UNIQUE1 __macro_internal_34bba35b8b9b20a75f9881e3795630e25d36e620d9c9741e2e9141ba82ec6ef7__
diff --git a/dyn_array.c b/dyn_array.c
index 0c5d627..fd8bcd9 100644
--- a/dyn_array.c
+++ b/dyn_array.c
@@ -39,7 +39,7 @@ static inline void *todo_remove_create_func(dyn_array_create_non_crashing_func_a
 		args.file,
 		args.line
 	);
-	header->size = 0;
+	header->n_items = 0;
 	header->capacity = args.initial_capacity;
 	header->itemsize = args.itemsize;
 	header->allocator = args.allocator;
@@ -48,7 +48,7 @@ static inline void *todo_remove_create_func(dyn_array_create_non_crashing_func_a
 
 static inline void *todo_remove_grow_func(void *this, size_t n_new_items, const char *file, int line) {
 	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, this);
-	size_t new_size = header->size + n_new_items;
+	size_t new_size = header->n_items + n_new_items;
 
 	if (header->capacity < new_size) {
 		size_t cap_times_2 = header->capacity * 2;
@@ -65,7 +65,7 @@ static inline void *todo_remove_grow_func(void *this, size_t n_new_items, const
 		);
 		header->capacity = new_capacity;
 	}
-	header->size = new_size;
+	header->n_items = new_size;
 	return &header->bytes;
 }
 
@@ -80,18 +80,35 @@ void dyn_array_shrink_func(void *this, size_t n_items_to_remove, const char *fil
 		exit(1);
 	}
 	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, this);
-	header->size -= n_items_to_remove;
+	header->n_items -= n_items_to_remove;
 }
 
 size_t arr_len(void *this) {
 	if (this == NULL) { return 0; }
 	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, this);
-	return header->size;
+	return header->n_items;
 
 }
 
-size_t dyn_array_capacity(void *this) {
+size_t arr_cap(void *this) {
 	if (this == NULL) { return 0; }
 	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, this);
 	return header->capacity;
 }
+
+bool dyn_array_contains_func(void *this, uint8_t *value) {
+	dyn_array_header_t *header = PTR_FROM_FIELD_PTR(dyn_array_header_t, bytes, this);
+	for (size_t i = 0; i < header->n_items; i++) {
+		bool is_equal = true;
+		for (size_t off = 0; off < header->itemsize; off++) {
+			if (header->bytes[i*header->itemsize+off] != value[off]) {
+				is_equal = false;
+				break;
+			}
+		}
+		if (is_equal) {
+			return true;
+		}
+	}
+	return false;
+}
diff --git a/test_dynamic_array.c b/test_dynamic_array.c
index 96b7fad..8b470f5 100644
--- a/test_dynamic_array.c
+++ b/test_dynamic_array.c
@@ -50,3 +50,21 @@ Test(dynamic_arrays, pop) {
 		}
 	}
 }
+
+Test(dynamic_arrays, contains) {
+	with_borrow(alloc) {
+		int *numbers = make_arr(alloc, int);
+		arr_append(numbers, 20);
+		cr_expect(arr_contains(numbers, int, 20));
+		arr_reset(numbers);
+
+		for ( size_t y = 0; y < 1000; y++ ) {
+			for ( size_t i = 0; i < 100; i++ ) {
+				if (!arr_contains(numbers, int, i)) {
+					arr_append(numbers, i);
+				}
+			}
+		}
+		cr_assert_eq(arr_len(numbers), 100);
+	}
+}