std.fmt.format — with streams

lib/std/buffer.zig

@@ -65,13 +65,9 @@ pub const Buffer = struct {
     }
 
     pub fn allocPrint(allocator: *Allocator, comptime format: []const u8, args: var) !Buffer {
-        const countSize = struct {
-            fn countSize(size: *usize, bytes: []const u8) (error{}!void) {
-                size.* += bytes.len;
-            }
-        }.countSize;
-        var size: usize = 0;
-        std.fmt.format(&size, error{}, countSize, format, args) catch |err| switch (err) {};
+        const size = std.fmt.count(format, args) catch |err| switch (err) {
+            error.Overflow => return error.OutOfMemory,
+        };
         var self = try Buffer.initSize(allocator, size);
         assert((std.fmt.bufPrint(self.list.items, format, args) catch unreachable).len == size);
         return self;
@@ -155,7 +151,7 @@ pub const Buffer = struct {
     }
 
     pub fn print(self: *Buffer, comptime fmt: []const u8, args: var) !void {
-        return std.fmt.format(self, error{OutOfMemory}, Buffer.append, fmt, args);
+        return self.outStream().print(fmt, args);
     }
 
     pub fn outStream(self: *Buffer) std.io.OutStream(*Buffer, error{OutOfMemory}, appendWrite) {

lib/std/builtin.zig

@@ -436,19 +436,17 @@ pub const Version = struct {
         self: Version,
         comptime fmt: []const u8,
         options: std.fmt.FormatOptions,
-        context: var,
-        comptime Error: type,
-        comptime output: fn (@TypeOf(context), []const u8) Error!void,
-    ) Error!void {
+        out_stream: var,
+    ) !void {
         if (fmt.len == 0) {
             if (self.patch == 0) {
                 if (self.minor == 0) {
-                    return std.fmt.format(context, Error, output, "{}", .{self.major});
+                    return std.fmt.format(out_stream, "{}", .{self.major});
                 } else {
-                    return std.fmt.format(context, Error, output, "{}.{}", .{ self.major, self.minor });
+                    return std.fmt.format(out_stream, "{}.{}", .{ self.major, self.minor });
                 }
             } else {
-                return std.fmt.format(context, Error, output, "{}.{}.{}", .{ self.major, self.minor, self.patch });
+                return std.fmt.format(out_stream, "{}.{}.{}", .{ self.major, self.minor, self.patch });
             }
         } else {
             @compileError("Unknown format string: '" ++ fmt ++ "'");

lib/std/fifo.zig

@@ -294,7 +294,19 @@ pub fn LinearFifo(
         pub usingnamespace if (T == u8)
             struct {
                 pub fn print(self: *Self, comptime format: []const u8, args: var) !void {
-                    return std.fmt.format(self, error{OutOfMemory}, Self.write, format, args);
+                    // TODO: maybe expose this stream as a method?
+                    const FifoStream = struct {
+                        const OutStream = std.io.OutStream(*Self, Error, write);
+                        const Error = error{OutOfMemory};
+
+                        fn write(fifo: *Self, bytes: []const u8) Error!usize {
+                            try fifo.write(bytes);
+                            return bytes.len;
+                        }
+                    };
+
+                    var out_stream = FifoStream.OutStream{ .context = self };
+                    try out_stream.print(format, args);
                 }
             }
         else