only accept single loader

config.go

@@ -66,31 +66,29 @@ func New(opts ...Option) *Config {
 	return (*Config)(option)
 }
 
-// Load loads configuration from the given loaders.
+// Load loads configuration from the given loader.
 // Each loader takes precedence over the loaders before it.
 //
 // This method can be called multiple times but it is not concurrency-safe.
-// It panics if any loader is nil.
-func (c *Config) Load(loaders ...Loader) error {
-	for i, loader := range loaders {
-		if loader == nil {
-			panic(fmt.Sprintf("cannot load config from nil loader at loaders[%d]", i))
-		}
+// It panics if loader is nil.
+func (c *Config) Load(loader Loader) error {
+	if loader == nil {
+		panic("cannot load config from nil loader")
+	}
 
-		values, err := loader.Load()
-		if err != nil {
-			return fmt.Errorf("load configuration: %w", err)
-		}
-		maps.Merge(c.values, values)
+	values, err := loader.Load()
+	if err != nil {
+		return fmt.Errorf("load configuration: %w", err)
+	}
+	maps.Merge(c.values, values)
 
-		provider := &provider{
-			loader: loader,
-			values: make(map[string]any),
-		}
-		// Merged to empty map to convert to lower case.
-		maps.Merge(provider.values, values)
-		c.providers = append(c.providers, provider)
+	provider := &provider{
+		loader: loader,
+		values: make(map[string]any),
 	}
+	// Merged to empty map to convert to lower case.
+	maps.Merge(provider.values, values)
+	c.providers = append(c.providers, provider)
 
 	return nil
 }

config_test.go

@@ -105,8 +105,9 @@ func TestConfig_Unmarshal(t *testing.T) {
 			t.Parallel()
 
 			config := konf.New(testcase.opts...)
-			err := config.Load(testcase.loaders...)
-			assert.NoError(t, err)
+			for _, loader := range testcase.loaders {
+				assert.NoError(t, config.Load(loader))
+			}
 			testcase.assert(config)
 		})
 	}
@@ -125,7 +126,9 @@ func (m mapLoader) String() string {
 func TestConfig_Explain(t *testing.T) {
 	t.Setenv("CONFIG_NEST", "env")
 	config := konf.New()
-	err := config.Load(env.New(), mapLoader{"owner": "map", "config": map[string]any{"nest": "map"}})
+	err := config.Load(env.New())
+	assert.NoError(t, err)
+	err = config.Load(mapLoader{"owner": "map", "config": map[string]any{"nest": "map"}})
 	assert.NoError(t, err)
 
 	assert.Equal(t, "non-exist has no configuration.\n\n", config.Explain("non-exist"))

example_test.go

@@ -43,11 +43,11 @@ var testdata embed.FS
 
 func ExampleSetDefault() {
 	config := konf.New()
-	err := config.Load(
-		kfs.New(testdata, "testdata/config.json"),
-		env.New(env.WithPrefix("server")),
-	)
-	if err != nil {
+	if err := config.Load(kfs.New(testdata, "testdata/config.json")); err != nil {
+		// Handle error here.
+		panic(err)
+	}
+	if err := config.Load(env.New(env.WithPrefix("server"))); err != nil {
 		// Handle error here.
 		panic(err)
 	}