diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 8c65ad2688..020ddfd7f7 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2081,8 +2081,13 @@ pub fn (mut c Checker) method_call(mut call_expr ast.CallExpr) ast.Type {
 		c.error('optional type cannot be called directly', call_expr.left.position())
 		return ast.void_type
 	}
-	if left_type_sym.kind in [.sum_type, .interface_] && method_name == 'type_name' {
-		return ast.string_type
+	if left_type_sym.kind in [.sum_type, .interface_] {
+		if method_name == 'type_name' {
+			return ast.string_type
+		}
+		if method_name == 'type_idx' {
+			return ast.int_type
+		}
 	}
 	if left_type == ast.void_type {
 		c.error('`void` type has no methods', call_expr.left.position())
@@ -3374,10 +3379,12 @@ pub fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 				return ast.int_type
 			}
 			else {
-				if node.field_name != 'name' {
-					c.error('invalid field `.$node.field_name` for type `$node.expr`',
-						node.pos)
+				if node.field_name == 'name' {
+					return ast.string_type
+				} else if node.field_name == 'idx' {
+					return ast.int_type
 				}
+				c.error('invalid field `.$node.field_name` for type `$node.expr`', node.pos)
 				return ast.string_type
 			}
 		}
@@ -8007,6 +8014,8 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.error('method overrides built-in array method', node.pos)
 		} else if sym.kind == .sum_type && node.name == 'type_name' {
 			c.error('method overrides built-in sum type method', node.pos)
+		} else if sym.kind == .sum_type && node.name == 'type_idx' {
+			c.error('method overrides built-in sum type method', node.pos)
 		} else if sym.kind == .multi_return {
 			c.error('cannot define method on multi-value', node.method_type_pos)
 		}
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index d483e75d0a..d5ade09750 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -528,7 +528,7 @@ pub fn (mut g Gen) finish() {
 pub fn (mut g Gen) write_typeof_functions() {
 	g.writeln('')
 	g.writeln('// >> typeof() support for sum types / interfaces')
-	for typ in g.table.type_symbols {
+	for ityp, typ in g.table.type_symbols {
 		if typ.kind == .sum_type {
 			sum_info := typ.info as ast.SumType
 			if sum_info.is_generic {
@@ -554,6 +554,26 @@ pub fn (mut g Gen) write_typeof_functions() {
 				g.writeln('\t}')
 			}
 			g.writeln('}')
+			g.writeln('')
+			g.writeln('int v_typeof_sumtype_idx_${typ.cname}(int sidx) { /* $typ.name */ ')
+			if g.pref.build_mode == .build_module {
+				g.writeln('\t\tif( sidx == _v_type_idx_${typ.cname}() ) return ${int(ityp)};')
+				for v in sum_info.variants {
+					subtype := g.table.get_type_symbol(v)
+					g.writeln('\tif( sidx == _v_type_idx_${subtype.cname}() ) return ${int(v)};')
+				}
+				g.writeln('\treturn ${int(ityp)};')
+			} else {
+				tidx := g.table.find_type_idx(typ.name)
+				g.writeln('\tswitch(sidx) {')
+				g.writeln('\t\tcase $tidx: return ${int(ityp)};')
+				for v in sum_info.variants {
+					g.writeln('\t\tcase $v: return ${int(v)};')
+				}
+				g.writeln('\t\tdefault: return ${int(ityp)};')
+				g.writeln('\t}')
+			}
+			g.writeln('}')
 		} else if typ.kind == .interface_ {
 			inter_info := typ.info as ast.Interface
 			if inter_info.is_generic {
@@ -566,6 +586,14 @@ pub fn (mut g Gen) write_typeof_functions() {
 			}
 			g.writeln('\treturn "unknown ${util.strip_main_name(typ.name)}";')
 			g.writeln('}')
+			g.writeln('')
+			g.writeln('int v_typeof_interface_idx_${typ.cname}(int sidx) { /* $typ.name */ ')
+			for t in inter_info.types {
+				subtype := g.table.get_type_symbol(t)
+				g.writeln('\tif (sidx == _${typ.cname}_${subtype.cname}_index) return ${int(t)};')
+			}
+			g.writeln('\treturn ${int(ityp)};')
+			g.writeln('}')
 		}
 	}
 	g.writeln('// << typeof() support for sum types')
@@ -3663,6 +3691,10 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 					// typeof(expr).name
 					g.type_name(node.name_type)
 					return
+				} else if node.field_name == 'idx' {
+					// typeof(expr).idx
+					g.write(int(g.unwrap_generic(node.name_type)).str())
+					return
 				}
 				g.error('unknown generic field', node.pos)
 			}
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 52df03a41e..7838221489 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -628,6 +628,13 @@ fn (mut g Gen) call_expr(node ast.CallExpr) {
 	}
 }
 
+fn (mut g Gen) conversion_function_call(prefix string, postfix string, node ast.CallExpr) {
+	g.write('${prefix}( (')
+	g.expr(node.left)
+	dot := if node.left_type.is_ptr() { '->' } else { '.' }
+	g.write(')${dot}_typ )$postfix')
+}
+
 fn (mut g Gen) method_call(node ast.CallExpr) {
 	// TODO: there are still due to unchecked exprs (opt/some fn arg)
 	if node.left_type == 0 {
@@ -744,20 +751,33 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 		return
 	}
 
-	if left_sym.kind == .sum_type && node.name == 'type_name' {
-		g.write('charptr_vstring_literal( /* $left_sym.name */ v_typeof_sumtype_${typ_sym.cname}( (')
-		g.expr(node.left)
-		dot := if node.left_type.is_ptr() { '->' } else { '.' }
-		g.write(')${dot}_typ ))')
-		return
-	}
-	if left_sym.kind == .interface_ && node.name == 'type_name' {
-		g.write('charptr_vstring_literal( /* $left_sym.name */ v_typeof_interface_${typ_sym.cname}( (')
-		g.expr(node.left)
-		dot := if node.left_type.is_ptr() { '->' } else { '.' }
-		g.write(')${dot}_typ ))')
-		return
+	if left_sym.kind in [.sum_type, .interface_] {
+		if node.name == 'type_name' {
+			if left_sym.kind == .sum_type {
+				g.conversion_function_call('charptr_vstring_literal( /* $left_sym.name */ v_typeof_sumtype_$typ_sym.cname',
+					')', node)
+				return
+			}
+			if left_sym.kind == .interface_ {
+				g.conversion_function_call('charptr_vstring_literal( /* $left_sym.name */ v_typeof_interface_$typ_sym.cname',
+					')', node)
+				return
+			}
+		}
+		if node.name == 'type_idx' {
+			if left_sym.kind == .sum_type {
+				g.conversion_function_call('/* $left_sym.name */ v_typeof_sumtype_idx_$typ_sym.cname',
+					'', node)
+				return
+			}
+			if left_sym.kind == .interface_ {
+				g.conversion_function_call('/* $left_sym.name */ v_typeof_interface_idx_$typ_sym.cname',
+					'', node)
+				return
+			}
+		}
 	}
+
 	if node.name == 'str' {
 		mut rec_type := node.receiver_type
 		if rec_type.has_flag(.shared_f) {
diff --git a/vlib/v/parser/struct.v b/vlib/v/parser/struct.v
index f282b5168b..7cd4e606e6 100644
--- a/vlib/v/parser/struct.v
+++ b/vlib/v/parser/struct.v
@@ -514,8 +514,8 @@ fn (mut p Parser) interface_decl() ast.InterfaceDecl {
 			line_nr := p.tok.line_nr
 			name := p.check_name()
 
-			if name == 'type_name' {
-				p.error_with_pos('cannot override built-in method `type_name`', method_start_pos)
+			if name in ['type_name', 'type_idx'] {
+				p.error_with_pos('cannot override built-in method `$name`', method_start_pos)
 				return ast.InterfaceDecl{}
 			}
 			if ts.has_method(name) {
diff --git a/vlib/v/tests/type_idx_test.v b/vlib/v/tests/type_idx_test.v
new file mode 100644
index 0000000000..aa8fb0bb45
--- /dev/null
+++ b/vlib/v/tests/type_idx_test.v
@@ -0,0 +1,101 @@
+// NB: .type_name() and .type_idx() called on an interface instance are more expensive
+// than typeof(instance).name and typeof(instance).idx, since they will search and return
+// the name and type index of the concrete interface instance.
+//
+// typeof(interface_instance).name returns the interface name, in the example here it will
+// be always 'Animal'.
+//
+// interface_instance.type_name() will return 'Dog' or 'Cat' in this example, depending on
+// what instance it is called.
+//
+// Similarly, typeof(interface_instance).idx will always return the same type index for all
+// kinds of Animal.
+
+interface Animal {
+	name string
+}
+
+struct Dog {
+	name string
+}
+
+struct Cat {
+	name string
+}
+
+type SumType = int | string
+
+fn test_type_idx() {
+	d := Dog{
+		name: 'Carlos'
+	}
+	c := Cat{
+		name: 'Tom'
+	}
+	ad := Animal(d)
+	ac := Animal(c)
+	dump(ad)
+	dump(ac)
+	divider___()
+	dump(typeof(ad).name)
+	dump(typeof(ac).name)
+	assert typeof(ad).name == 'Animal'
+	assert typeof(ac).name == 'Animal'
+	dump(typeof(ad).idx)
+	dump(typeof(ac).idx)
+	assert typeof(ad).idx == typeof(ac).idx
+	divider___()
+	dump(ad.type_name())
+	dump(ac.type_name())
+	assert ad.type_name() == 'Dog'
+	assert ac.type_name() == 'Cat'
+	dump(ad.type_idx())
+	dump(ac.type_idx())
+	assert ad.type_idx() != ac.type_idx()
+	assert ac.type_idx() != typeof(ad).idx
+	divider___()
+	dump(typeof(d).name)
+	dump(typeof(c).name)
+	assert typeof(d).name == 'Dog'
+	assert typeof(c).name == 'Cat'
+	dump(typeof(d).idx)
+	dump(typeof(c).idx)
+	assert typeof(d).idx != typeof(c).idx
+	assert typeof(d).idx != typeof(ad).idx
+}
+
+fn test_sumtype_type_idx() {
+	s := 'abc'
+	i := 123
+	ss := SumType(s)
+	si := SumType(i)
+	divider___()
+	dump(s)
+	dump(i)
+	dump(ss)
+	dump(si)
+	dump(typeof(s).idx)
+	dump(typeof(i).idx)
+	dump(typeof(ss).idx)
+	dump(typeof(si).idx)
+	assert typeof(ss).idx != typeof(s).idx
+	assert typeof(s).idx != typeof(i).idx
+	assert typeof(ss).idx == typeof(si).idx
+	divider___()
+	dump(ss.type_name())
+	dump(si.type_name())
+	assert ss.type_name() == 'string'
+	assert si.type_name() == 'int'
+	assert ss.type_name() != si.type_name()
+	dump(ss.type_idx())
+	dump(si.type_idx())
+	assert ss.type_idx() == typeof(s).idx
+	assert si.type_idx() == typeof(i).idx
+	assert ss.type_idx() != si.type_idx()
+	assert typeof(ss).idx != ss.type_idx()
+	assert typeof(si).idx != si.type_idx()
+}
+
+fn divider___() {
+	println('------------------------------------------------------------')
+}