Use method to set defaults on config

build.go

@@ -49,7 +49,7 @@ type xbuilder struct {
 }
 
 // Build creates a new xtemplate server instance, a `CancelHandler`, from an xtemplate.Config.
-func Build(config *Config) (CancelHandler, error) {
+func Build(config Config) (CancelHandler, error) {
 	builder, err := newBuilder(config)
 	if err != nil {
 		return nil, err
@@ -105,24 +105,16 @@ func Build(config *Config) (CancelHandler, error) {
 var nextInstanceIdentity int64
 
 // newBuilder creates an empty xserver with all data structures initalized using the provided config.
-func newBuilder(config *Config) (*xbuilder, error) {
+func newBuilder(config Config) (*xbuilder, error) {
+	config.FillDefaults()
 	server := &xserver{
-		Config: *config,
+		Config: config,
 	}
 
 	if server.Template.FS == nil {
-		if server.Template.Path == "" {
-			server.Template.Path = "templates"
-			config.Template.Path = "templates"
-		}
 		server.Template.FS = os.DirFS(server.Template.Path)
 	}
 
-	if server.Template.TemplateExtension == "" {
-		server.Template.TemplateExtension = ".html"
-		config.Template.TemplateExtension = ".html"
-	}
-
 	if server.Context.FS == nil && server.Context.Path != "" {
 		server.Context.FS = os.DirFS(server.Context.Path)
 	}

config.go

@@ -11,9 +11,7 @@ import (
 
 func New() (c *Config) {
 	c = &Config{}
-	c.Template.Path = "templates"
-	c.UserConfig = make(map[string]string)
-	c.Template.TemplateExtension = ".html"
+	c.FillDefaults()
 	return
 }
 
@@ -70,14 +68,40 @@ type Config struct {
 	LogLevel int          `json:"log_level,omitempty"`
 }
 
+// UserConfig are key-value pairs made available to the template context as .Config
 type UserConfig map[string]string
 
-func (c *Config) WithTemplateFS(fs fs.FS) {
-	c.Template.FS = fs
+// FillDefaults sets default values for unset fields
+func (config *Config) FillDefaults() {
+	if config.Template.Path == "" {
+		config.Template.Path = "templates"
+	}
+
+	if config.Template.TemplateExtension == "" {
+		config.Template.TemplateExtension = ".html"
+	}
+
+	if config.Template.Delimiters.Left == "" {
+		config.Template.Delimiters.Left = "{{"
+	}
+
+	if config.Template.Delimiters.Right == "" {
+		config.Template.Delimiters.Right = "}}"
+	}
+
+	if config.UserConfig == nil {
+		config.UserConfig = make(map[string]string)
+	}
 }
 
 type override func(*Config)
 
+func WithTemplateFS(fs fs.FS) override {
+	return func(c *Config) {
+		c.Template.FS = fs
+	}
+}
+
 func WithContextFS(fs fs.FS) override {
 	return func(c *Config) {
 		c.Context.FS = fs

main.go

@@ -57,6 +57,7 @@ var helptext = `xtemplate is a hypertext preprocessor and html templating http s
 `
 
 func parseflags() (f flags) {
+	f.config = *New()
 	flag.StringVar(&f.listen_addr, "listen", "0.0.0.0:8080", "Listen address")
 	flag.StringVar(&f.config.Template.Path, "template-path", "templates", "Directory where templates are loaded from")
 	flag.BoolVar(&f.watch_template_path, "watch-template", true, "Watch the template directory and reload if changed")
@@ -91,7 +92,7 @@ func Main(overrides ...override) {
 	for _, o := range overrides {
 		o(&flags.config)
 	}
-	handler, err := Build(&flags.config)
+	handler, err := Build(flags.config)
 	if err != nil {
 		log.Error("failed to load xtemplate", slog.Any("error", err))
 		os.Exit(2)
@@ -113,7 +114,7 @@ func Main(overrides ...override) {
 		if len(watchDirs) != 0 {
 			_, err := watch.Watch(watchDirs, 200*time.Millisecond, log.WithGroup("fswatch"), func() bool {
 				log := log.With(slog.Group("reload", slog.Int64("current_id", handler.Id())))
-				temphandler, err := Build(&flags.config)
+				temphandler, err := Build(flags.config)
 				if err != nil {
 					log.Info("failed to reload xtemplate", slog.Any("error", err))
 				} else {