Unify error handling with static error variables

markdown.go

@@ -1,7 +1,6 @@
 package termhyo
 
 import (
-	"fmt"
 	"strings"
 )
 
@@ -27,7 +26,7 @@ func hasAutoWidth(table *Table) bool {
 // AddRow adds a row for markdown rendering (buffered mode for width calculation).
 func (r *MarkdownRenderer) AddRow(_ *Table, row Row) error {
 	if r.rendered {
-		return fmt.Errorf("cannot add rows after table is rendered")
+		return ErrAddAfterRender
 	}
 
 	// Buffer the row for width calculation
@@ -40,7 +39,7 @@ func (r *MarkdownRenderer) AddRow(_ *Table, row Row) error {
 // Render renders any remaining content (for streaming, this is just cleanup).
 func (r *MarkdownRenderer) Render(table *Table) error {
 	if r.rendered {
-		return fmt.Errorf("table already rendered")
+		return ErrTableAlreadyRendered
 	}
 
 	// Calculate column widths if needed using all buffered rows

renderer.go

@@ -1,7 +1,5 @@
 package termhyo
 
-import "fmt"
-
 // Renderer defines the interface for different rendering strategies.
 type Renderer interface {
 	AddRow(table *Table, row Row) error
@@ -39,7 +37,7 @@ type Buffered struct {
 // AddRow adds a row to the buffered renderer.
 func (r *Buffered) AddRow(table *Table, row Row) error {
 	if r.rendered {
-		return fmt.Errorf("cannot add rows after table is rendered")
+		return ErrAddAfterRender
 	}
 	// Store row for later rendering
 	table.rows = append(table.rows, row)
@@ -49,7 +47,7 @@ func (r *Buffered) AddRow(table *Table, row Row) error {
 // Render renders the buffered content all at once.
 func (r *Buffered) Render(table *Table) error {
 	if r.rendered {
-		return fmt.Errorf("table already rendered")
+		return ErrTableAlreadyRendered
 	}
 
 	// Calculate column widths for auto-width columns
@@ -88,7 +86,7 @@ type Streaming struct {
 // AddRow adds a row to the streaming renderer.
 func (r *Streaming) AddRow(table *Table, row Row) error {
 	if r.rendered {
-		return fmt.Errorf("cannot add rows after table is rendered")
+		return ErrAddAfterRender
 	}
 
 	if !r.headerDone {
@@ -104,7 +102,7 @@ func (r *Streaming) AddRow(table *Table, row Row) error {
 // Render renders the streaming content, typically just the footer.
 func (r *Streaming) Render(table *Table) error {
 	if r.rendered {
-		return fmt.Errorf("table already rendered")
+		return ErrTableAlreadyRendered
 	}
 
 	// For streaming mode, just render footer

table.go

@@ -1,10 +1,24 @@
 package termhyo
 
 import (
+	"errors"
 	"io"
 	"strings"
 )
 
+var (
+	// ErrNoColumns is returned when trying to render a table with no columns defined.
+	ErrNoColumns = errors.New("no columns defined")
+	// ErrNoHeader is returned when trying to render a table without a header.
+	ErrNoHeader = errors.New("header is required")
+	// ErrNoMarkdownHeader is returned when trying to render a markdown table without a header.
+	ErrNoMarkdownHeader = errors.New("markdown table requires at least one non-empty header")
+	// ErrTableAlreadyRendered is returned when trying to render a table that has already been rendered.
+	ErrTableAlreadyRendered = errors.New("table has already been rendered")
+	// ErrAddAfterRender is returned when trying to add a row after rendering.
+	ErrAddAfterRender = errors.New("cannot add row after table has been rendered")
+)
+
 // TableOption is a functional option for configuring Table.
 type TableOption func(*Table)
 
@@ -59,7 +73,7 @@ func (t *Table) GetAlign() bool {
 //
 // Example:
 //
-//	table := termhyo.NewTable(os.Stdout, columns, termhyo.Border(termhyo.DoubleStyle), termhyo.Align(false))
+//	table := termhyo.NewTable(os.Stdout, columns, termhyo.Border(termhyo.DoubleStyle), termhyo.AutoAlign(false))
 //
 // This is the recommended way to create and configure tables in termhyo.
 func NewTable(writer io.Writer, columns []Column, opts ...TableOption) *Table {
@@ -223,6 +237,9 @@ func (t *Table) CalculateColumnWidths() {
 
 // RenderHeader renders the table header.
 func (t *Table) RenderHeader() error {
+	if len(t.columns) == 0 {
+		return ErrNoColumns
+	}
 	// Top border (only if enabled)
 	if t.borderConfig.Top {
 		if err := t.RenderBorderLine("top"); err != nil {