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package cty
// Walk visits all of the values in a possibly-complex structure, calling
// a given function for each value.
//
// For example, given a list of strings the callback would first be called
// with the whole list and then called once for each element of the list.
//
// The callback function may prevent recursive visits to child values by
// returning false. The callback function my halt the walk altogether by
// returning a non-nil error. If the returned error is about the element
// currently being visited, it is recommended to use the provided path
// value to produce a PathError describing that context.
//
// The path passed to the given function may not be used after that function
// returns, since its backing array is re-used for other calls.
func Walk(val Value, cb func(Path, Value) (bool, error)) error {
var path Path
return walk(path, val, cb)
}
func walk(path Path, val Value, cb func(Path, Value) (bool, error)) error {
deeper, err := cb(path, val)
if err != nil {
return err
}
if !deeper {
return nil
}
if val.IsNull() || !val.IsKnown() {
// Can't recurse into null or unknown values, regardless of type
return nil
}
ty := val.Type()
switch {
case ty.IsObjectType():
for it := val.ElementIterator(); it.Next(); {
nameVal, av := it.Element()
path := append(path, GetAttrStep{
Name: nameVal.AsString(),
})
err := walk(path, av, cb)
if err != nil {
return err
}
}
case val.CanIterateElements():
for it := val.ElementIterator(); it.Next(); {
kv, ev := it.Element()
path := append(path, IndexStep{
Key: kv,
})
err := walk(path, ev, cb)
if err != nil {
return err
}
}
}
return nil
}
// Transform visits all of the values in a possibly-complex structure,
// calling a given function for each value which has an opportunity to
// replace that value.
//
// Unlike Walk, Transform visits child nodes first, so for a list of strings
// it would first visit the strings and then the _new_ list constructed
// from the transformed values of the list items.
//
// This is useful for creating the effect of being able to make deep mutations
// to a value even though values are immutable. However, it's the responsibility
// of the given function to preserve expected invariants, such as homogenity of
// element types in collections; this function can panic if such invariants
// are violated, just as if new values were constructed directly using the
// value constructor functions. An easy way to preserve invariants is to
// ensure that the transform function never changes the value type.
//
// The callback function my halt the walk altogether by
// returning a non-nil error. If the returned error is about the element
// currently being visited, it is recommended to use the provided path
// value to produce a PathError describing that context.
//
// The path passed to the given function may not be used after that function
// returns, since its backing array is re-used for other calls.
func Transform(val Value, cb func(Path, Value) (Value, error)) (Value, error) {
var path Path
return transform(path, val, cb)
}
func transform(path Path, val Value, cb func(Path, Value) (Value, error)) (Value, error) {
ty := val.Type()
var newVal Value
switch {
case val.IsNull() || !val.IsKnown():
// Can't recurse into null or unknown values, regardless of type
newVal = val
case ty.IsListType() || ty.IsSetType() || ty.IsTupleType():
l := val.LengthInt()
switch l {
case 0:
// No deep transform for an empty sequence
newVal = val
default:
elems := make([]Value, 0, l)
for it := val.ElementIterator(); it.Next(); {
kv, ev := it.Element()
path := append(path, IndexStep{
Key: kv,
})
newEv, err := transform(path, ev, cb)
if err != nil {
return DynamicVal, err
}
elems = append(elems, newEv)
}
switch {
case ty.IsListType():
newVal = ListVal(elems)
case ty.IsSetType():
newVal = SetVal(elems)
case ty.IsTupleType():
newVal = TupleVal(elems)
default:
panic("unknown sequence type") // should never happen because of the case we are in
}
}
case ty.IsMapType():
l := val.LengthInt()
switch l {
case 0:
// No deep transform for an empty map
newVal = val
default:
elems := make(map[string]Value)
for it := val.ElementIterator(); it.Next(); {
kv, ev := it.Element()
path := append(path, IndexStep{
Key: kv,
})
newEv, err := transform(path, ev, cb)
if err != nil {
return DynamicVal, err
}
elems[kv.AsString()] = newEv
}
newVal = MapVal(elems)
}
case ty.IsObjectType():
switch {
case ty.Equals(EmptyObject):
// No deep transform for an empty object
newVal = val
default:
atys := ty.AttributeTypes()
newAVs := make(map[string]Value)
for name := range atys {
av := val.GetAttr(name)
path := append(path, GetAttrStep{
Name: name,
})
newAV, err := transform(path, av, cb)
if err != nil {
return DynamicVal, err
}
newAVs[name] = newAV
}
newVal = ObjectVal(newAVs)
}
default:
newVal = val
}
return cb(path, newVal)
}
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