Add Sub() for Viper, which returns a branch of a Viper instance.
diff --git a/README.md b/README.md
index b081df9..8c592b1 100644
--- a/README.md
+++ b/README.md
@@ -441,6 +441,52 @@
GetString("datastore.metric.host") //returns "0.0.0.0"
```
+### Extract sub-tree
+
+Extract sub-tree from Viper.
+
+For example, `viper` represents:
+
+```json
+app:
+ cache1:
+ max-items: 100
+ item-size: 64
+ cache2:
+ max-items: 200
+ item-size: 80
+```
+
+After executing:
+
+```go
+subv := viper.Sub("app.cache1")
+```
+
+`subv` represents:
+
+```json
+max-items: 100
+item-size: 64
+```
+
+Suppose we have:
+
+```go
+func NewCache(cfg *Viper) *Cache {...}
+```
+
+which creates a cache based on config information formatted as `subv`.
+Now it's easy to create these 2 caches separately as:
+
+```go
+cfg1 := viper.Sub("app.cache1")
+cache1 := NewCache(cfg1)
+
+cfg2 := viper.Sub("app.cache2")
+cache2 := NewCache(cfg2)
+```
+
### Unmarshaling
You also have the option of Unmarshaling all or a specific value to a struct, map,
diff --git a/viper.go b/viper.go
index 6f204b1..a671c1f 100644
--- a/viper.go
+++ b/viper.go
@@ -513,6 +513,18 @@
return val
}
+// Returns new Viper instance representing a sub tree of this instance
+func Sub(key string) *Viper { return v.Sub(key) }
+func (v *Viper) Sub(key string) *Viper {
+ data, ok := v.Get(key).(map[string]interface{})
+ if !ok {
+ return nil
+ }
+ subv := New()
+ subv.config = data
+ return subv
+}
+
// Returns the value associated with the key as a string
func GetString(key string) string { return v.GetString(key) }
func (v *Viper) GetString(key string) string {
diff --git a/viper_test.go b/viper_test.go
index bfbfcec..0c71549 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -724,3 +724,16 @@
// been ignored by the client, the default still loads
assert.Equal(t, `default`, v.GetString(`key`))
}
+
+func TestSub(t *testing.T) {
+ v := New()
+ v.SetConfigType("yaml")
+ v.ReadConfig(bytes.NewBuffer(yamlExample))
+
+ subv := v.Sub("clothing.pants")
+ assert.Equal(t, v.Get("clothing.pants.size"), subv.Get("size"))
+
+ subv = v.Sub("clothing.pants.size")
+ assert.Equal(t, subv, (*Viper)(nil))
+}
+
