Refactor dynamic memory allocation interface

src/core/io.zig

@@ -4,67 +4,47 @@ const stack = @import("./stack.zig");
 const testing = @import("./testing.zig");
 
 ///
-/// Dynamic memory allocation interface.
 ///
-pub const Allocator = union (enum) {
-    bound: struct {
-        alloc: fn (usize) ?[*]u8,
-        dealloc: fn ([*]u8) void,
-    },
-
-    arena: struct {
-        buffer: []u8,
-        cursor: usize = 0,
-    },
-
 ///
-    /// [MakeError.OutOfMemory] is used to indicate there is not enough memory available for a given
-    /// operation.
-    ///
-    pub const MakeError = error {
-        OutOfMemory,
+pub const Allocation = struct {
+    existing: ?[*]u8,
+    size: usize
 };
 
 ///
-    /// Frees `allocation` using `allocator`.
+/// Dynamic memory allocation interface.
 ///
-    pub fn free(allocator: *Allocator, allocation: anytype) void {
-        switch (@typeInfo(@TypeOf(allocation))) {
-            .Pointer => |pointer| if (pointer.size == .Slice)
-                @compileError("`allocation` cannot be a slice"),
-
-            else => @compileError("`allocation` must be a pointer"),
-        }
-
-        if (@typeInfo(@TypeOf(allocation)) != .Pointer)
-            @compileError("`allocation` must be a pointer");
-
-        // TODO: Implement arena de-allocation.
-        switch (allocator.*) {
-            .bound => |bound| bound.dealloc(@ptrCast([*]u8, allocation)),
-            .arena => {},
-        }
-    }
+pub const Allocator = meta.Function(Allocation, ?[*]u8);
 
 ///
-    /// Attempts to allocate `size` number of `Element`s using `allocator`.
 ///
-    /// Returns the allocation or a [MakeError] if it failed.
 ///
-    pub fn make(allocator: *Allocator, comptime Element: type, size: usize) MakeError![*]Element {
-        switch (allocator.*) {
-            .bound => |bound| return @ptrCast([*]Element, @alignCast(@alignOf(Element),
-                bound.alloc(@sizeOf(Element) * size) orelse return error.OutOfMemory)),
+pub const ArenaAllocator = struct {
+    region: []u8,
+    cursor: usize = 0,
 
-            .arena => |*stack| {
-                defer stack.cursor += size;
+    ///
+    ///
+    ///
+    pub fn allocator(arena_allocator: *ArenaAllocator) Allocator {
+        return Allocator.fromClosure(arena_allocator, struct {
+            fn call(context: *ArenaAllocator, allocation: Allocation) ?[*]u8 {
+                _ = allocation;
+                _ = context;
 
-                return @ptrCast([*]Element, @alignCast(@alignOf(Element), stack.buffer.ptr));
-            },
+                return null;
             }
+        }.call);
     }
 };
 
+///
+///
+///
+pub const MakeError = error {
+    OutOfMemory,
+};
+
 ///
 /// Closure that captures a reference to readable resources like block devices, memory buffers,
 /// network sockets, and more.
@@ -337,6 +317,24 @@ test "Find first of sequence" {
     try testing.expect(findFirstOf([]const u8, haystack, &.{"baz", "bar"}, testEquality) == null);
 }
 
+///
+///
+///
+pub fn free(allocator: Allocator, allocated_memory: anytype) void {
+    if (allocator.call(.{
+        .existing = @ptrCast([*]u8, switch (@typeInfo(@TypeOf(allocated_memory))) {
+            .Pointer => |info| switch (info.size) {
+                .One, .Many, .C => allocated_memory,
+                .Slice => allocated_memory.ptr,
+            },
+
+            else => @compileError("`allocated_memory` must be a pointer"),
+        }),
+
+        .size = 0,
+    }) != null) unreachable;
+}
+
 ///
 /// Returns a deterministic hash code compiled from each byte in `bytes`.
 ///
@@ -357,6 +355,16 @@ test "Hashing bytes" {
     try testing.expect(hashBytes(bytes_sequence) != hashBytes(&.{69, 42}));
 }
 
+///
+///
+///
+pub fn makeMany(comptime Element: type, allocator: Allocator, size: usize) MakeError![*]Element {
+    return @ptrCast([*]Element, @alignCast(@alignOf(Element), allocator.call(.{
+        .existing = null,
+        .size = size,
+    }) orelse return error.OutOfMemory));
+}
+
 ///
 /// Swaps the `Data` in `this` with `that`.
 ///

src/core/stack.zig

@@ -113,7 +113,7 @@ test "Fixed stack of string literals" {
 ///
 /// Potential errors that may occur while trying to push one or more elements into a stack.
 ///
-pub const PushError = io.Allocator.MakeError;
+pub const PushError = io.MakeError;
 
 ///
 /// Returns an [io.Writer] wrapping `fixed_stack`.

src/core/table.zig

@@ -11,7 +11,7 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
     const Allocator = io.Allocator;
 
     return struct {
-        allocator: *Allocator,
+        allocator: Allocator,
         load_limit: f32,
         buckets: []Bucket,
         filled: usize,
@@ -37,7 +37,7 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
         /// Deinitializes `self`, preventing any further use.
         ///
         pub fn deinit(self: *Self) void {
-            self.allocator.free(self.buckets.ptr);
+            io.free(self.allocator, self.buckets);
 
             self.buckets = &.{};
         }
@@ -45,13 +45,13 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
         ///
         /// Initializes a [Self] using `allocator` as the memory allocation strategy.
         ///
-        /// Returns a new [Self] value or an [io.Allocator.MakeError] if initializing failed.
+        /// Returns a new [Self] value or an [io.MakeError] if initializing failed.
         ///
-        pub fn init(allocator: *Allocator) Allocator.MakeError!Self {
+        pub fn init(allocator: Allocator) io.MakeError!Self {
             const initial_capacity = 4;
 
             return Self{
-                .buckets = (try allocator.make(Bucket, initial_capacity))[0 .. initial_capacity],
+                .buckets = (try io.makeMany(Bucket, allocator, initial_capacity))[0 .. initial_capacity],
                 .filled = 0,
                 .allocator = allocator,
                 .load_limit = 0.75,
@@ -99,11 +99,12 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
             if (self.loadFactor() >= self.load_limit) {
                 const old_buckets = self.buckets;
 
-                defer self.allocator.free(old_buckets.ptr);
+                defer io.free(self.allocator, old_buckets);
 
                 const bucket_count = old_buckets.len * 2;
 
-                self.buckets = (try self.allocator.make(Bucket, bucket_count))[0 .. bucket_count];
+                self.buckets = (try io.makeMany(Bucket, self.allocator,
+                    bucket_count))[0 .. bucket_count];
 
                 for (old_buckets) |bucket, index| self.buckets[index] = bucket;
             }
@@ -163,7 +164,7 @@ pub fn Hashed(comptime Key: type, comptime Value: type,
 /// [InsertError.KeyExists] occurs when an insertion was attempted on a table with a matching key
 /// already present.
 ///
-pub const InsertError = io.Allocator.MakeError || error {
+pub const InsertError = io.MakeError || error {
     KeyExists,
 };
 
@@ -197,8 +198,10 @@ pub const string_literal_context = KeyContext([]const u8){
 
 test "Hash table manipulation with string literal context" {
     var buffer = [_]u8{0} ** 1024;
-    var allocator = io.Allocator{.arena = .{.buffer = &buffer}};
-    var table = try Hashed([]const u8, u32, string_literal_context).init(&allocator);
+    var arena_allocator = io.ArenaAllocator{.region = &buffer};
+
+    var table =
+        try Hashed([]const u8, u32, string_literal_context).init(arena_allocator.allocator());
 
     defer table.deinit();