gen: more efficient `for in` with a map (#6961)

vlib/v/gen/cgen.v

@@ -1173,33 +1173,34 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 	} else if it.kind == .map {
 		// `for key, val in map {`
 		g.writeln('// FOR IN map')
-		key_styp := g.typ(it.key_type)
-		val_styp := g.typ(it.val_type)
-		val_sym := g.table.get_type_symbol(it.val_type)
-		keys_tmp := 'keys_' + g.new_tmp_var()
 		idx := g.new_tmp_var()
-		key := if it.key_var in ['', '_'] { g.new_tmp_var() } else { it.key_var }
-		zero := g.type_default(it.val_type)
 		atmp := g.new_tmp_var()
 		atmp_styp := g.typ(it.cond_type)
 		g.write('$atmp_styp $atmp = ')
 		g.expr(it.cond)
 		g.writeln(';')
-		g.writeln('array_$key_styp $keys_tmp = map_keys(&$atmp);')
-		g.writeln('for (int $idx = 0; $idx < ${keys_tmp}.len; ++$idx) {')
+		g.writeln('for (int $idx = 0; $idx < $atmp\.key_values.len; ++$idx) {')
+		g.writeln('\tif ($atmp\.key_values.keys[$idx].str == 0) {continue;}')
+		if it.key_var != '_' {
+			key_styp := g.typ(it.key_type)
+			key := c_name(it.key_var)
 			// TODO: analyze whether it.key_type has a .clone() method and call .clone() for all types:
 			if it.key_type == table.string_type {
-			g.writeln('\t$key_styp $key = /*kkkk*/ string_clone( (($key_styp*)${keys_tmp}.data)[$idx] );')
+				g.writeln('\t$key_styp $key = /*kkkk*/ string_clone($atmp\.key_values.keys[$idx]);')
 			} else {
-			g.writeln('\t$key_styp $key = /*kkkk*/ (($key_styp*)${keys_tmp}.data)[$idx];')
+				g.writeln('\t$key_styp $key = /*kkkk*/ $atmp\.key_values.keys[$idx];')
+			}
 		}
 		if it.val_var != '_' {
+			val_sym := g.table.get_type_symbol(it.val_type)
+			valstr := '(void*)($atmp\.key_values.values + $idx * (u32)($atmp\.value_bytes))'
 			if val_sym.kind == .function {
 				g.write('\t')
 				g.write_fn_ptr_decl(val_sym.info as table.FnType, c_name(it.val_var))
-				g.writeln(' = (*(voidptr*)map_get($atmp, $key, &(voidptr[]){ $zero }));')
+				g.writeln(' = (*(voidptr*)$valstr);')
 			} else {
-				g.writeln('\t$val_styp ${c_name(it.val_var)} = (*($val_styp*)map_get($atmp, $key, &($val_styp[]){ $zero }));')
+				val_styp := g.typ(it.val_type)
+				g.writeln('\t$val_styp ${c_name(it.val_var)} = (*($val_styp*)$valstr);')
 			}
 		}
 		g.stmts(it.stmts)
@@ -1213,9 +1214,6 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 		if it.label.len > 0 {
 			g.writeln('\t$it.label\__break: {}')
 		}
-		g.writeln('/*for in map cleanup*/')
-		g.writeln('for (int $idx = 0; $idx < ${keys_tmp}.len; ++$idx) { string_free(&(($key_styp*)${keys_tmp}.data)[$idx]); }')
-		g.writeln('array_free(&$keys_tmp);')
 		return
 	} else if it.cond_type.has_flag(.variadic) {
 		g.writeln('// FOR IN cond_type/variadic')

vlib/v/tests/blank_ident_test.v

@@ -103,9 +103,11 @@ fn test_for_in_map_val() {
 }
 
 fn test_for_in_map_both() {
+	mut i := 0
 	for _, _ in m {
-		assert true
+		i++
 	}
+	assert i == 1
 }
 
 fn test_nested_for_in_map_key() {
@@ -127,11 +129,13 @@ fn test_nested_for_in_map_val() {
 }
 
 fn test_nested_for_in_map_both() {
+	mut i := 0
 	for _, _ in m {
 		for _, _ in m {
-			assert true
+			i++
 		}
 	}
+	assert i == 1
 }
 
 fn fn_for_in_variadic_args_simple(arr ...string) {

vlib/v/tests/for_loops_test.v

@@ -43,16 +43,24 @@ fn test_for_char_in_string() {
 	assert sum == 394 // ascii codes of `a` + `b` + `c` + `d`
 }
 
-fn test_for_char_in_map() {
+fn test_for_string_in_map() {
 	m := {
 		'a': 'b'
 		'c': 'd'
 	}
 	mut acc := ''
-	for k, char in m {
-		acc += '$k: $char, '
+	for k, v in m {
+		acc += '$k: $v, '
 	}
 	assert acc == 'a: b, c: d, '
+
+	mut m2 := {'a': 3, 'b': 4, 'c': 5}
+	m2.delete('b')
+	acc = ''
+	for k, v in m2 {
+		acc += '$k: $v, '
+	}
+	assert acc == 'a: 3, c: 5, '
 }
 
 fn test_mut_for() {