Add Path.Index helper method (#56)
An analysis of user code shows that Path.Last was not sufficient and
that what users really wanted was an easy want to do negative indexing
without needing to constantly check for out-of-bounds.
Thus, add a generic Index method that does not panic on out-of-bounds
accesses and supports negative indexing.
diff --git a/cmp/cmpopts/ignore.go b/cmp/cmpopts/ignore.go
index 016891d..e86554b 100644
--- a/cmp/cmpopts/ignore.go
+++ b/cmp/cmpopts/ignore.go
@@ -50,7 +50,7 @@
if len(p) < 1 {
return false
}
- t := p[len(p)-1].Type()
+ t := p.Last().Type()
for _, ti := range tf {
if t.AssignableTo(ti) {
return true
@@ -95,7 +95,7 @@
if len(p) < 1 {
return false
}
- t := p[len(p)-1].Type()
+ t := p.Last().Type()
for _, ti := range tf {
if t.AssignableTo(ti) {
return true
@@ -131,14 +131,11 @@
return ux
}
func (xf unexportedFilter) filter(p cmp.Path) bool {
- if len(p) < 2 {
- return false
- }
- sf, ok := p[len(p)-1].(cmp.StructField)
+ sf, ok := p.Index(-1).(cmp.StructField)
if !ok {
return false
}
- return xf.m[p[len(p)-2].Type()] && !isExported(sf.Name())
+ return xf.m[p.Index(-2).Type()] && !isExported(sf.Name())
}
// isExported reports whether the identifier is exported.
diff --git a/cmp/path.go b/cmp/path.go
index 76d73f7..13d9c2e 100644
--- a/cmp/path.go
+++ b/cmp/path.go
@@ -94,10 +94,21 @@
// Last returns the last PathStep in the Path.
// If the path is empty, this returns a non-nil PathStep that reports a nil Type.
func (pa Path) Last() PathStep {
- if len(pa) > 0 {
- return pa[len(pa)-1]
+ return pa.Index(-1)
+}
+
+// Index returns the ith step in the Path and supports negative indexing.
+// A negative index starts counting from the tail of the Path such that -1
+// refers to the last step, -2 refers to the second-to-last step, and so on.
+// If index is invalid, this returns a non-nil PathStep that reports a nil Type.
+func (pa Path) Index(i int) PathStep {
+ if i < 0 {
+ i = len(pa) + i
}
- return pathStep{}
+ if i < 0 || i >= len(pa) {
+ return pathStep{}
+ }
+ return pa[i]
}
// String returns the simplified path to a node.
