op, internal/ops: cleanups

Remove unnecessary fill when starting a recording in op.Record.
Have the exact number of possible stack kinds in ops.Ops.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

internal/ops/ops.go

@@ -26,7 +26,7 @@ type Ops struct {
 	multipOp bool
 
 	macroStack stack
-	stacks     [5]stack
+	stacks     [_StackKind]stack
 }
 
 type OpType byte
@@ -80,7 +80,7 @@ type StackID struct {
 	prev int
 }
 
-// StateOp represents a saved operation snapshop to be restored
+// StateOp represents a saved operation snapshot to be restored
 // later.
 type StateOp struct {
 	id      int
@@ -108,7 +108,7 @@ const (
 	ClipStack StackKind = iota
 	TransStack
 	PassStack
-	MetaStack
+	_StackKind
 )
 
 const (
@@ -180,9 +180,7 @@ func (op *ClipOp) Decode(data []byte) {
 
 func Reset(o *Ops) {
 	o.macroStack = stack{}
-	for i := range o.stacks {
-		o.stacks[i] = stack{}
-	}
+	o.stacks = [_StackKind]stack{}
 	// Leave references to the GC.
 	for i := range o.refs {
 		o.refs[i] = nil

op/op.go

@@ -153,8 +153,8 @@ func Record(o *Ops) MacroOp {
 		pc:  ops.PCFor(&o.Internal),
 	}
 	// Reserve room for a macro definition. Updated in Stop.
-	ops.Write(m.ops, ops.TypeMacroLen)
-	m.fill()
+	data := ops.Write(m.ops, ops.TypeMacroLen)
+	data[0] = byte(ops.TypeMacro)
 	return m
 }
 
@@ -162,17 +162,13 @@ func Record(o *Ops) MacroOp {
 // operation for replaying it.
 func (m MacroOp) Stop() CallOp {
 	ops.PopMacro(m.ops, m.id)
-	m.fill()
+	ops.FillMacro(m.ops, m.pc)
 	return CallOp{
 		ops: m.ops,
 		pc:  m.pc,
 	}
 }
 
-func (m MacroOp) fill() {
-	ops.FillMacro(m.ops, m.pc)
-}
-
 // Add the recorded list of operations. Add
 // panics if the Ops containing the recording
 // has been reset.