println: optimize and remove memory leaks

compiler/fn.v

@@ -670,7 +670,7 @@ fn (p mut Parser) fn_call_args(f *Fn) *Fn {
 		if i == f.args.len - 1 && arg.name == '..' {
 			break
 		}
-		amp_ph := p.cgen.add_placeholder()
+		ph := p.cgen.add_placeholder()
 		// ) here means not enough args were supplied
 		if p.tok == RPAR {
 			str_args := f.str_args(p.table)// TODO this is C args
@@ -688,18 +688,21 @@ fn (p mut Parser) fn_call_args(f *Fn) *Fn {
 			p.check(MUT)
 		}
 		typ := p.bool_expression()
-		// TODO temporary hack to allow println(777)
+		// Optimize `println`: replace it with `printf` to avoid extra allocations and
+		// function calls. `println(777)` => `printf("%d\n", 777)` 
+		// (If we don't check for void, then V will compile `println(func())`) 
 		if i == 0 && f.name == 'println' && typ != 'string' && typ != 'void' {
-			// If we dont check for void, then V will compile "println(procedure())"
 			T := p.table.find_type(typ)
-			if typ == 'u8' {
-				p.cgen.set_placeholder(amp_ph, 'u8_str(')
-			}
-			else if T.parent == 'int' {
-				p.cgen.set_placeholder(amp_ph, 'int_str(')
+			fmt := p.typ_to_fmt(typ) 
+			if fmt != '' { 
+				p.cgen.cur_line = p.cgen.cur_line.replace('println (', '/*opt*/printf ("' + fmt + '", ')    
+				continue 
+			}  
+			if T.parent == 'int' {
+				p.cgen.set_placeholder(ph, 'int_str(')
 			}
 			else if typ.ends_with('*') {
-				p.cgen.set_placeholder(amp_ph, 'ptr_str(')
+				p.cgen.set_placeholder(ph, 'ptr_str(')
 			}
 			else {
 				// Make sure this type has a `str()` method
@@ -719,7 +722,7 @@ fn (p mut Parser) fn_call_args(f *Fn) *Fn {
 					}
 					p.error('`$typ` needs to have method `str() string` to be printable')
 				}
-				p.cgen.set_placeholder(amp_ph, '${typ}_str(')
+				p.cgen.set_placeholder(ph, '${typ}_str(')
 			}
 			p.gen(')')
 			continue
@@ -737,7 +740,7 @@ fn (p mut Parser) fn_call_args(f *Fn) *Fn {
 		if !is_interface {
 			// Dereference
 			if got.contains('*') && !expected.contains('*') {
-				p.cgen.set_placeholder(amp_ph, '*')
+				p.cgen.set_placeholder(ph, '*')
 			}
 			// Reference
 			// TODO ptr hacks. DOOM hacks, fix please.
@@ -746,14 +749,14 @@ fn (p mut Parser) fn_call_args(f *Fn) *Fn {
 				if ! (expected == 'void*' && got == 'int') &&
 				! (expected == 'byte*' && got.contains(']byte')) &&
 				! (expected == 'byte*' && got == 'string') {
-					p.cgen.set_placeholder(amp_ph, '& /*11 EXP:"$expected" GOT:"$got" */')
+					p.cgen.set_placeholder(ph, '& /*11 EXP:"$expected" GOT:"$got" */')
 				}
 			}
 		}
 		// interface?
 		if is_interface {
 			if !got.contains('*') {
-				p.cgen.set_placeholder(amp_ph, '&')
+				p.cgen.set_placeholder(ph, '&')
 			}
 			// Pass all interface methods
 			interface_type := p.table.find_type(arg.typ)

compiler/parser.v

@@ -2149,7 +2149,6 @@ fn (p mut Parser) typ_to_fmt(typ string) string {
 		if typ.ends_with('*') {
 			return '%p' 
 		} 
-		p.error('unhandled sprintf format "$typ" ')
 	}
 	return ''
 }
@@ -2214,17 +2213,22 @@ fn (p mut Parser) string_expr() {
 			p.next()
 		}
 		else {
-			format += p.typ_to_fmt(typ)
+			f := p.typ_to_fmt(typ)
+			if f == '' { 
+				p.error('unhandled sprintf format "$typ" ')
+			} 
+			format += f 
 		}
 	}
 	// println("hello %d", num) optimization.
 	if p.cgen.nogen {
 		return
 	}
-	// Don't allocate a new string, just print	it. TODO HACK PRINT OPT
+	// println: don't allocate a new string, just print	it. 
 	cur_line := p.cgen.cur_line.trim_space()
-	if cur_line.contains('println(') && p.tok != PLUS && !p.pref.is_prod && !cur_line.contains('string_add') {
-		p.cgen.cur_line = cur_line.replace('println(', 'printf(')
+	if cur_line.contains('println (') && p.tok != PLUS && 
+		!cur_line.contains('string_add') && !cur_line.contains('eprintln') {
+		p.cgen.cur_line = cur_line.replace('println (', 'printf(')
 		p.gen('$format\\n$args')
 		return
 	}

compiler/tests/struct_test.v

@@ -8,6 +8,7 @@ struct B{
 mut: 
 	a A 
 } 
+
 struct C {
 mut: 
 	b B 
@@ -15,6 +16,11 @@ mut:
 	as []A 
 	num int 
 } 
+
+struct User {
+	name string
+	age int 
+} 
  
 fn test_struct_levels() { 
 	mut c := C{} 
@@ -42,3 +48,9 @@ fn test_struct_levels() {
 	c.as[0].val  = 10 
 	assert c.as[0].val == 10 
 } 
+
+fn test_struct_str() {
+	u := User{'Bob', 30} 
+	println(u)  // make sure the struct is printable 
+	// assert u.str() == '{name:"Bob", age:30}'  // TODO 
+}