feat: allow struct slice and struct array for valueType (#70)

* feat: allow struct slice and struct array for to determine Header

csvutil.go

@@ -154,7 +154,7 @@ func countRecords(s []byte) (n int) {
 	}
 }
 
-// Header scans the provided struct type and generates a CSV header for it.
+// Header scans the provided struct type, struct slice or struct array and generates a CSV header for it.
 //
 // Field names are written in the same order as struct fields are defined.
 // Embedded struct's fields are treated as if they were part of the outer struct.
@@ -175,8 +175,8 @@ func countRecords(s []byte) (n int) {
 //
 // If tag is left empty the default "csv" will be used.
 //
-// Header will return UnsupportedTypeError if the provided value is nil or is
-// not a struct.
+// Header will return UnsupportedTypeError if the provided value is nil, is
+// not a struct, a struct slice or a struct array.
 func Header(v any, tag string) ([]string, error) {
 	typ, err := valueType(v)
 	if err != nil {
@@ -216,10 +216,15 @@ loop:
 	}
 
 	typ := walkType(val.Type())
-	if typ.Kind() != reflect.Struct {
-		return nil, &UnsupportedTypeError{Type: typ}
+	switch typ.Kind() {
+	case reflect.Struct:
+		return typ, nil
+	case reflect.Slice, reflect.Array:
+		if eTyp := walkType(typ.Elem()); eTyp.Kind() == reflect.Struct {
+			return eTyp, nil
+		}
 	}
-	return typ, nil
+	return nil, &UnsupportedTypeError{Type: typ}
 }
 
 func newCSVReader(r io.Reader) *csv.Reader {

csvutil_test.go

@@ -627,10 +627,64 @@ func TestHeader(t *testing.T) {
 			err:  &UnsupportedTypeError{Type: reflect.TypeOf(int(0))},
 		},
 		{
-			desc: "slice",
-			v:    []TypeJ{{}},
+			desc:   "slice",
+			v:      []TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc:   "ptr slice",
+			v:      &[]TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc:   "slice with ptr value",
+			v:      []*TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc: "slice with non-struct",
+			v:    []int{0},
+			tag:  "csv",
+			err:  &UnsupportedTypeError{Type: reflect.TypeOf([]int{0})},
+		},
+		{
+			desc: "two-dimensional slice",
+			v:    [][]TypeJ{{{}}},
+			tag:  "csv",
+			err:  &UnsupportedTypeError{Type: reflect.TypeOf([][]TypeJ{{}})},
+		},
+		{
+			desc:   "array",
+			v:      [1]TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc:   "ptr array",
+			v:      &[1]TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc:   "array with ptr value",
+			v:      [1]*TypeJ{{}},
+			tag:    "csv",
+			header: []string{"STR", "int", "Bool", "Uint8", "float"},
+		},
+		{
+			desc: "array with non-struct",
+			v:    [1]int{0},
+			tag:  "csv",
+			err:  &UnsupportedTypeError{Type: reflect.TypeOf([1]int{0})},
+		},
+		{
+			desc: "two-dimensional array",
+			v:    [1][1]TypeJ{{{}}},
 			tag:  "csv",
-			err:  &UnsupportedTypeError{Type: reflect.TypeOf([]TypeJ{})},
+			err:  &UnsupportedTypeError{Type: reflect.TypeOf([1][1]TypeJ{{}})},
 		},
 		{
 			desc: "nil interface",

encoder_test.go

@@ -1778,6 +1778,46 @@ func TestEncoder(t *testing.T) {
 					},
 				},
 			},
+			{
+				desc: "struct slice",
+				in:   []TypeF{},
+				out: [][]string{
+					{
+						"int",
+						"pint",
+						"int8",
+						"pint8",
+						"int16",
+						"pint16",
+						"int32",
+						"pint32",
+						"int64",
+						"pint64",
+						"uint",
+						"puint",
+						"uint8",
+						"puint8",
+						"uint16",
+						"puint16",
+						"uint32",
+						"puint32",
+						"uint64",
+						"puint64",
+						"float32",
+						"pfloat32",
+						"float64",
+						"pfloat64",
+						"string",
+						"pstring",
+						"bool",
+						"pbool",
+						"interface",
+						"pinterface",
+						"binary",
+						"pbinary",
+					},
+				},
+			},
 			{
 				desc: "ptr to nil interface",
 				in:   &nilIface,