Ensured precdence with a test, added documentation

README.md

@@ -53,6 +53,35 @@ func main() {
 }
 ```
 
+### Provide variable defaults by using a file
+
+Given you have a file `~/.myapp.yml` containing some secrets or usernames (for the example below username is assumed to be "luzifer") as a default configuration for your application you can use this source code to load the defaults from that file using the `vardefault` tag in your configuration struct.
+
+The order of the directives (lower number = higher precedence):
+
+1. Flags provided in command line
+1. Environment variables
+1. Variable defaults (`vardefault` tag in the struct)
+1. `default` tag in the struct
+
+```go
+type config struct {
+  Username string `vardefault:"username" flag:"username" description:"Your username"`
+}
+
+var cfg = config{}
+
+func init() {
+  rconfig.SetVariableDefaults(VarDefaultsFromYAMLFile("~/.myapp.yml"))
+  rconfig.Parse(&cfg)
+}
+
+func main() {
+  fmt.Printf("Username = %s", cfg.Username)
+  // Output: Username = luzifer
+}
+```
+
 ## More info
 
 You can see the full reference documentation of the rconfig package [at godoc.org](https://godoc.org/github.com/Luzifer/rconfig), or through go's standard documentation system by running `godoc -http=:6060` and browsing to [http://localhost:6060/pkg/github.com/Luzifer/rconfig](http://localhost:6060/pkg/github.com/Luzifer/rconfig) after installation.

config.go

@@ -91,8 +91,8 @@ func execTags(in interface{}, fs *pflag.FlagSet) error {
 			continue
 		}
 
-		value := envDefault(typeField.Tag.Get("env"), typeField.Tag.Get("default"))
+		value := varDefault(typeField.Tag.Get("vardefault"), typeField.Tag.Get("default"))
-		value = varDefault(typeField.Tag.Get("vardefault"), value)
+		value = envDefault(typeField.Tag.Get("env"), value)
 		parts := strings.Split(typeField.Tag.Get("flag"), ",")
 
 		switch typeField.Type.Kind() {

precedence_test.go

@@ -0,0 +1,87 @@
+package rconfig
+
+import (
+	"os"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Precedence", func() {
+
+	type t struct {
+		A int `default:"1" vardefault:"a" env:"a" flag:"avar,a" description:"a"`
+	}
+
+	var (
+		err         error
+		cfg         t
+		args        []string
+		vardefaults map[string]string
+	)
+
+	JustBeforeEach(func() {
+		cfg = t{}
+		SetVariableDefaults(vardefaults)
+		err = parse(&cfg, args)
+	})
+
+	Context("Provided: Flag, Env, Default, VarDefault", func() {
+		BeforeEach(func() {
+			args = []string{"-a", "5"}
+			os.Setenv("a", "8")
+			vardefaults = map[string]string{
+				"a": "3",
+			}
+		})
+
+		It("should not have errored", func() { Expect(err).NotTo(HaveOccurred()) })
+		It("should have used the flag value", func() {
+			Expect(cfg.A).To(Equal(5))
+		})
+	})
+
+	Context("Provided: Env, Default, VarDefault", func() {
+		BeforeEach(func() {
+			args = []string{}
+			os.Setenv("a", "8")
+			vardefaults = map[string]string{
+				"a": "3",
+			}
+		})
+
+		It("should not have errored", func() { Expect(err).NotTo(HaveOccurred()) })
+		It("should have used the env value", func() {
+			Expect(cfg.A).To(Equal(8))
+		})
+	})
+
+	Context("Provided: Default, VarDefault", func() {
+		BeforeEach(func() {
+			args = []string{}
+			os.Unsetenv("a")
+			vardefaults = map[string]string{
+				"a": "3",
+			}
+		})
+
+		It("should not have errored", func() { Expect(err).NotTo(HaveOccurred()) })
+		It("should have used the vardefault value", func() {
+			Expect(cfg.A).To(Equal(3))
+		})
+	})
+
+	Context("Provided: Default", func() {
+		BeforeEach(func() {
+			args = []string{}
+			os.Unsetenv("a")
+			vardefaults = map[string]string{}
+		})
+
+		It("should not have errored", func() { Expect(err).NotTo(HaveOccurred()) })
+		It("should have used the default value", func() {
+			Expect(cfg.A).To(Equal(1))
+		})
+	})
+
+})