implement the stringer interface

.gitignore

@@ -0,0 +1 @@
+.idea

duration.go

@@ -10,13 +10,14 @@ import (
 
 // Duration holds all the smaller units that make up the duration
 type Duration struct {
-	Years   float64
-	Months  float64
-	Weeks   float64
-	Days    float64
-	Hours   float64
-	Minutes float64
-	Seconds float64
+	originalString string
+	Years          float64
+	Months         float64
+	Weeks          float64
+	Days           float64
+	Hours          float64
+	Minutes        float64
+	Seconds        float64
 }
 
 const (
@@ -33,7 +34,9 @@ var (
 // if parsing fails an error is returned instead
 func Parse(d string) (*Duration, error) {
 	state := parsingPeriod
-	duration := &Duration{}
+	duration := &Duration{
+		originalString: d,
+	}
 	num := ""
 	var err error
 
@@ -137,3 +140,8 @@ func (duration *Duration) ToTimeDuration() time.Duration {
 
 	return timeDuration
 }
+
+// String returns the duration string from which the *Duration was parsed
+func (duration *Duration) String() string {
+	return duration.originalString
+}

duration_test.go

@@ -20,28 +20,31 @@ func TestParse(t *testing.T) {
 			name: "period-only",
 			args: args{d: "P4Y"},
 			want: &Duration{
-				Years: 4,
+				originalString: "P4Y",
+				Years:          4,
 			},
 			wantErr: false,
 		},
 		{
 			name: "time-only-decimal",
 			args: args{d: "T2.5S"},
 			want: &Duration{
-				Seconds: 2.5,
+				originalString: "T2.5S",
+				Seconds:        2.5,
 			},
 			wantErr: false,
 		},
 		{
 			name: "full",
 			args: args{d: "P3Y6M4DT12H30M5.5S"},
 			want: &Duration{
-				Years:   3,
-				Months:  6,
-				Days:    4,
-				Hours:   12,
-				Minutes: 30,
-				Seconds: 5.5,
+				originalString: "P3Y6M4DT12H30M5.5S",
+				Years:          3,
+				Months:         6,
+				Days:           4,
+				Hours:          12,
+				Minutes:        30,
+				Seconds:        5.5,
 			},
 			wantErr: false,
 		},
@@ -130,3 +133,14 @@ func TestDuration_ToTimeDuration(t *testing.T) {
 		})
 	}
 }
+
+func TestDuration_String(t *testing.T) {
+	duration, err := Parse("P3Y6M4DT12H30M5.5S")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if duration.String() != "P3Y6M4DT12H30M5.5S" {
+		t.Errorf("expected: %s, got: %s", "P3Y6M4DT12H30M5.5S", duration.String())
+	}
+}