compiler: blank identifier for loops. dont declare any variables

compiler/fn.v

@@ -543,11 +543,10 @@ fn (p mut Parser) check_unused_variables() {
 		if var.name == '' {
 			break
 		}
-		if !var.is_used && !p.pref.is_repl && !var.is_arg && !p.pref.translated && var.name != '_' {
+		if !var.is_used && !p.pref.is_repl && !var.is_arg && !p.pref.translated {
 			p.production_error('`$var.name` declared and not used', var.scanner_pos )
 		}
-		if !var.is_changed && var.is_mut && !p.pref.is_repl &&
-			!p.pref.translated && var.name != '_' {
+		if !var.is_changed && var.is_mut && !p.pref.is_repl && !p.pref.translated {
 			p.error_with_position( '`$var.name` is declared as mutable, but it was never changed', var.scanner_pos )
 		}
 	}

compiler/gen_c.v

@@ -256,17 +256,20 @@ fn (p mut Parser) gen_array_at(typ_ string, is_arr0 bool, fn_ph int) {
 
 fn (p mut Parser) gen_for_header(i, tmp, var_typ, val string) {
 	p.genln('for (int $i = 0; $i < ${tmp}.len; $i++) {')
+	if val == '_' { return }
 	p.genln('$var_typ $val = (($var_typ *) $tmp . data)[$i];')
 }
 
 fn (p mut Parser) gen_for_str_header(i, tmp, var_typ, val string) {
 	p.genln('array_byte bytes_$tmp = string_bytes( $tmp );')
 	p.genln(';\nfor (int $i = 0; $i < $tmp .len; $i ++) {')
+	if val == '_' { return }
 	p.genln('$var_typ $val = (($var_typ *) bytes_$tmp . data)[$i];')
 }
 
 fn (p mut Parser) gen_for_range_header(i, range_end, tmp, var_type, val string) {
 	p.genln(';\nfor (int $i = $tmp; $i < $range_end; $i++) {')
+	if val == '_' { return }
 	p.genln('$var_type $val = $i;')
 }
 
@@ -277,6 +280,7 @@ fn (p mut Parser) gen_for_map_header(i, tmp, var_typ, val, typ string) {
 	p.genln('string $i = ((string*)keys_$tmp .data)[l];')
 	// TODO don't call map_get() for each key, fetch values while traversing
 	// the tree (replace `map_keys()` above with `map_key_vals()`)
+	if val == '_' { return }
 	p.genln('$var_typ $val = $def; map_get($tmp, $i, & $val);')
 }
 

compiler/gen_js.v

@@ -99,21 +99,25 @@ fn (p mut Parser) gen_array_at(typ string, is_arr0 bool, fn_ph int) {
 
 fn (p mut Parser) gen_for_header(i, tmp, var_typ, val string) {
 	p.genln('for (var $i = 0; $i < ${tmp}.length; $i++) {')
+	if val == '_' { return }
 	p.genln('var $val = $tmp [$i];')
 }
 
 fn (p mut Parser) gen_for_range_header(i, range_end, tmp, var_type, val string) {
 	p.genln(';\nfor (var $i = $tmp; $i < $range_end; $i++) {')
+	if val == '_' { return }
 	p.genln('var /*$var_type*/ $val = $i;')
 }
 
 fn (p mut Parser) gen_for_str_header(i, tmp, var_typ, val string) {
 	p.genln('for (var $i = 0; $i < $tmp .length; $i ++) {')
+	if val == '_' { return }
 	p.genln('var $val = $tmp[$i];')
 }
 
 fn (p mut Parser) gen_for_map_header(i, tmp, var_typ, val, typ string) {
 	p.genln('for (var $i in $tmp) {')
+	if val == '_' { return }
 	p.genln('var $val = $tmp[$i];')
 }
 

compiler/parser.v

@@ -3275,44 +3275,33 @@ fn (p mut Parser) for_st() {
 		pad := if is_arr { 6 } else  { 4 }
 		var_typ := if is_str { 'byte' } else { typ.right(pad) }
 		// typ = strings.Replace(typ, "_ptr", "*", -1)
-		// Register temp var
-		val_var := Var {
-			name: val
-			typ: var_typ
-			ptr: typ.contains('*')
-		}
-		p.register_var(val_var)
+		mut i_var_type := 'int'
 		if is_arr {
-			i_var := Var {
-				name: i
-				typ: 'int'
-				// parent_fn: p.cur_fn
-				is_mut: true
-				is_changed: true
-			}
-			//p.genln(';\nfor ($i_type $i = 0; $i < $tmp .len; $i ++) {')
 			p.gen_for_header(i, tmp, var_typ, val)
-			p.register_var(i_var)
 		}
 		else if is_map {
-			i_var := Var {
-				name: i
-				typ: 'string'
-				is_mut: true
-				is_changed: true
-			}
-			p.register_var(i_var)
+			i_var_type = 'string'
 			p.gen_for_map_header(i, tmp, var_typ, val, typ)
 		}
 		else if is_str {
-			i_var := Var {
+			i_var_type = 'byte'
+			p.gen_for_str_header(i, tmp, var_typ, val)
+		}
+		// Register temp vars
+		if i != '_' {
+			p.register_var(Var {
 				name: i
-				typ: 'byte'
+				typ: i_var_type
 				is_mut: true
 				is_changed: true
+			})
 		}
-			p.register_var(i_var)
-			p.gen_for_str_header(i, tmp, var_typ, val)
+		if val != '_' {
+			p.register_var(Var {
+				name: val
+				typ: var_typ
+				ptr: typ.contains('*')
+			})
 		}
 	}
 	// `for val in vals`
@@ -3357,13 +3346,14 @@ fn (p mut Parser) for_st() {
 		}
 		// println('for typ=$typ vartyp=$var_typ')
 		// Register temp var
-		val_var := Var {
+		if val != '_' {
+			p.register_var(Var {
 				name: val
 				typ: var_type
 				ptr: typ.contains('*')
 				is_changed: true
+			})
 		}
-		p.register_var(val_var)
 		i := p.get_tmp()
 		if is_arr {
 			p.gen_for_header(i, tmp, var_type, val)