Extract Ona IO writer into reusable "Function" type

src/ona/fmt.zig

@@ -0,0 +1,70 @@
+const io = @import("io.zig");
+
+///
+/// Number formatting modes supported by [writeInt].
+///
+pub const Radix = enum {
+    binary,
+    tinary,
+    quaternary,
+    quinary,
+    senary,
+    septenary,
+    octal,
+    nonary,
+    decimal,
+    undecimal,
+    duodecimal,
+    tridecimal,
+    tetradecimal,
+    pentadecimal,
+    hexadecimal,
+};
+
+///
+/// Writes `value` as a ASCII / UTF-8 encoded integer to `writer`, returning `true` if the full
+/// sequence was successfully written, otherwise `false`.
+///
+/// The `radix` argument identifies which base system to format `value` as.
+///
+pub fn printInt(writer: io.Writer, radix: Radix, value: anytype) bool {
+    const Int = @TypeOf(value);
+    const type_info = @typeInfo(Int);
+
+    switch (type_info) {
+        .Int => {
+            if (value == 0) return writer.writeByte('0');
+
+            // TODO: Unhardcode this as it will break with large ints.
+            var buffer = std.mem.zeroes([28]u8);
+            var buffer_count = @as(usize, 0);
+            var n1 = value;
+
+            if ((type_info.Int.signedness == .signed) and (value < 0)) {
+                // Negative value.
+                n1 = -value;
+                buffer[0] = '-';
+                buffer_count += 1;
+            }
+
+            while (n1 != 0) {
+                const base = @enumToInt(radix);
+
+                buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
+                n1 = (n1 / base);
+                buffer_count += 1;
+            }
+
+            for (buffer[0 .. (buffer_count / 2)]) |_, i|
+                std.mem.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
+
+            return (writer.call(.{buffer[0 .. buffer_count]}) == buffer_count);
+        },
+
+        // Cast comptime int into known-size integer and try again.
+        .ComptimeInt => return writer.
+            writeInt(radix, @intCast(std.math.IntFittingRange(value, value), value)),
+
+        else => @compileError("value must be of type int"),
+    }
+}

src/ona/io.zig

@@ -1,3 +1,4 @@
+const meta = @import("./meta.zig");
 const stack = @import("./stack.zig");
 const std = @import("std");
 
@@ -170,121 +171,9 @@ test "Spliterating text" {
 }
 
 ///
-/// Opaque interface to a "writable" resource, such as a block device, memory buffer, or network
-/// socket.
+/// Opaque interface to a "writable" resource like a block device, memory buffer, or network socket.
 ///
-pub const Writer = struct {
-    context: *anyopaque,
-    writeContext: fn (*anyopaque, []const u8) usize,
-
-    ///
-    /// Radices supported by [writeInt].
-    ///
-    pub const Radix = enum {
-        binary,
-        tinary,
-        quaternary,
-        quinary,
-        senary,
-        septenary,
-        octal,
-        nonary,
-        decimal,
-        undecimal,
-        duodecimal,
-        tridecimal,
-        tetradecimal,
-        pentadecimal,
-        hexadecimal,
-    };
-
-    ///
-    /// Wraps and returns a reference to `write_context` of type `WriteContext` and its associated
-    /// `writeContext` writing operation in a [Writer].
-    ///
-    pub fn wrap(
-        comptime WriteContext: type,
-        write_context: *WriteContext,
-        comptime writeContext: fn (*WriteContext, []const u8) usize
-    ) Writer {
-        return .{
-            .context = write_context,
-
-            .writeContext = struct {
-                fn write(context: *anyopaque, buffer: []const u8) usize {
-                    return writeContext(@ptrCast(*WriteContext,
-                        @alignCast(@alignOf(WriteContext), context)), buffer);
-                }
-            }.write,
-        };
-    }
-
-    ///
-    /// Attempts to write `buffer` to `writer`, returning the number of bytes from `buffer` that
-    /// were successfully written.
-    ///
-    pub fn write(writer: Writer, buffer: []const u8) usize {
-        return writer.writeContext(writer.context, buffer);
-    }
-
-    ///
-    /// Writes the singular `byte` to `writer`, returning `true` if it was successfully written,
-    /// otherwise `false`.
-    ///
-    pub fn writeByte(writer: Writer, byte: u8) bool {
-        return (writer.writeContext(writer.context,
-            @ptrCast([*]const u8, &byte)[0 .. 1]) != 0);
-    }
-
-    ///
-    /// Writes `value` as a ASCII / UTF-8 encoded integer to `writer`, returning `true` if the full
-    /// sequence was successfully written, otherwise `false`.
-    ///
-    /// The `radix` argument identifies which base system to encode `value` as, with `10` being
-    /// decimal, `16` being hexadecimal, `8` being octal`, so on and so forth.
-    ///
-    pub fn writeInt(writer: Writer, radix: Radix, value: anytype) bool {
-        const Int = @TypeOf(value);
-        const type_info = @typeInfo(Int);
-
-        switch (type_info) {
-            .Int => {
-                if (value == 0) return writer.writeByte('0');
-
-                // TODO: Unhardcode this as it will break with large ints.
-                var buffer = std.mem.zeroes([28]u8);
-                var buffer_count = @as(usize, 0);
-                var n1 = value;
-
-                if ((type_info.Int.signedness == .signed) and (value < 0)) {
-                    // Negative value.
-                    n1 = -value;
-                    buffer[0] = '-';
-                    buffer_count += 1;
-                }
-
-                while (n1 != 0) {
-                    const base = @enumToInt(radix);
-
-                    buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
-                    n1 = (n1 / base);
-                    buffer_count += 1;
-                }
-
-                for (buffer[0 .. (buffer_count / 2)]) |_, i|
-                    std.mem.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
-
-                return (writer.write(buffer[0 .. buffer_count]) == buffer_count);
-            },
-
-            // Cast comptime int into known-size integer and try again.
-            .ComptimeInt => return writer.
-                writeInt(radix, @intCast(std.math.IntFittingRange(value, value), value)),
-
-            else => @compileError("value must be of type int"),
-        }
-    }
-};
+pub const Writer = meta.Function([]const u8, usize);
 
 ///
 /// Returns `true` if `this_bytes` is the same length and contains the same data as `that_bytes`,
@@ -323,21 +212,19 @@ test "Hashing bytes" {
     try testing.expect(hashBytes(bytes_sequence) != hashBytes(&.{69, 42}));
 }
 
+var null_context: usize = undefined;
+
 ///
 /// Writer that silently throws consumed data away and never fails.
 ///
 /// This is commonly used for testing or redirected otherwise unwanted output data that can't not be
 /// sent somewhere for whatever reason.
 ///
-pub const null_writer = Writer{
-    .context = undefined,
-
-    .writeContext = struct {
-        fn write(_: *anyopaque, buffer: []const u8) usize {
+pub const null_writer = Writer.wrap(&null_context, struct {
+    fn write(_: *@TypeOf(null_context), buffer: []const u8) usize {
         return buffer.len;
     }
-    }.write,
-};
+}.write);
 
 test "Null writing" {
     const testing = std.testing;
@@ -345,9 +232,14 @@ test "Null writing" {
     {
         const sequence = "foo";
 
-        try testing.expectEqual(null_writer.write(sequence), sequence.len);
+        try testing.expectEqual(null_writer.apply(sequence), sequence.len);
     }
-
-    try testing.expect(null_writer.writeByte(0));
-    try testing.expect(null_writer.writeInt(.decimal, 420));
+}
+
+///
+/// Writes the singular `byte` to `writer`, returning `true` if it was successfully written,
+/// otherwise `false`.
+///
+pub fn writeByte(writer: Writer, byte: u8) bool {
+    return (writer.call(.{@ptrCast([*]const u8, &byte)[0 .. 1]}) != 0);
 }

src/ona/meta.zig

@@ -8,3 +8,54 @@ pub fn FnReturn(comptime Fn: type) type {
 
     return type_info.Fn.return_type orelse void;
 }
+
+///
+/// Returns single-input closure type where `Input` is the input type and `Output` is the output
+/// type.
+///
+pub fn Function(comptime Input: type, comptime Output: type) type {
+    return struct {
+        context: *anyopaque,
+        contextualApply: fn (*anyopaque, Input) Output,
+
+        ///
+        /// Function type.
+        ///
+        const Self = @This();
+
+        ///
+        /// Applies `input` to `self`, producing a result according to the type-erased
+        /// implementation.
+        ///
+        pub fn apply(self: Self, input: Input) Output {
+            return self.contextualApply(self.context, input);
+        }
+
+        ///
+        /// Creates a new [Self] by wrapping `concrete_context` as a pointer to the implementation
+        /// and `contextualApply` as the behavior executed when [apply] is called.
+        ///
+        /// The newly created [Self] is returned.
+        ///
+        pub fn wrap(
+            concrete_context: anytype,
+            comptime contextualApply: fn (@TypeOf(concrete_context), Input) Output
+        ) Self {
+            const ConcreteContext = @TypeOf(concrete_context);
+
+            if (@typeInfo(ConcreteContext) != .Pointer)
+                @compileError("`concrete_context` must be a pointer type");
+
+            return .{
+                .context = concrete_context,
+
+                .contextualApply = struct {
+                    fn call(erased_context: *anyopaque, input: Input) Output {
+                        return contextualApply(@ptrCast(ConcreteContext, @alignCast(
+                            @alignOf(ConcreteContext), erased_context)), input);
+                    }
+                }.call,
+            };
+        }
+    };
+}

src/ona/stack.zig

@@ -23,7 +23,7 @@ pub fn Fixed(comptime Element: type) type {
             if (Element != u8) @compileError("Cannot coerce fixed stack of type " ++
                 @typeName(Element) ++ " into a Writer");
 
-            return io.Writer.wrap(Self, self, struct {
+            return io.Writer.wrap(self, struct {
                 fn write(stack: *Self, buffer: []const u8) usize {
                     stack.pushAll(buffer) catch |err| switch (err) {
                         error.OutOfMemory => return 0,
@@ -112,6 +112,5 @@ test "Fixed stack manipulation" {
 
     const writer = stack.writer();
 
-    try testing.expectEqual(writer.write(&.{0, 0, 0, 0}), 4);
-    try testing.expectEqual(writer.writeByte(0), false);
+    try testing.expectEqual(writer.apply(&.{0, 0, 0, 0}), 4);
 }