From 65711ac33659f8da3ef31065df745a90815b7c71 Mon Sep 17 00:00:00 2001
From: Mahendra Kanani <mgkanani.cse.iitb@gmail.com>
Date: Sat, 29 Jun 2019 13:43:53 +0530
Subject: [PATCH] Enhanced Gauge API (#106)

---
 stats.go      | 9 +++++++++
 stats_test.go | 8 ++++++++
 types.go      | 6 ++++++
 3 files changed, 23 insertions(+)

diff --git a/stats.go b/stats.go
index aba2f9e8..328c0448 100644
--- a/stats.go
+++ b/stats.go
@@ -118,6 +118,15 @@ func (g *gauge) Update(v float64) {
 	atomic.StoreUint64(&g.updated, 1)
 }
 
+func (g *gauge) Add(v float64) {
+	v += math.Float64frombits(atomic.LoadUint64(&g.curr))
+	g.Update(v)
+}
+
+func (g *gauge) Sub(v float64) {
+	g.Add(-v)
+}
+
 func (g *gauge) value() float64 {
 	return math.Float64frombits(atomic.LoadUint64(&g.curr))
 }
diff --git a/stats_test.go b/stats_test.go
index 96142fe4..ce87868a 100644
--- a/stats_test.go
+++ b/stats_test.go
@@ -108,6 +108,14 @@ func TestGauge(t *testing.T) {
 	gauge.report("", nil, r)
 	assert.Equal(t, float64(42), r.last)
 
+	gauge.Add(4.2)
+	gauge.report("", nil, r)
+	assert.Equal(t, float64(46.2), r.last)
+
+	gauge.Sub(-4)
+	gauge.report("", nil, r)
+	assert.Equal(t, float64(50.2), r.last)
+
 	gauge.Update(1234)
 	gauge.Update(5678)
 	gauge.report("", nil, r)
diff --git a/types.go b/types.go
index 14105c68..ec5b730b 100644
--- a/types.go
+++ b/types.go
@@ -69,6 +69,12 @@ type Counter interface {
 type Gauge interface {
 	// Update sets the gauges absolute value.
 	Update(value float64)
+
+	// Add updates gauges absolute value by adding 'value' to current value
+	Add(value float64)
+
+	// Sub updates gauges absolute value by subtracting 'value' from current value
+	Sub(value float64)
 }
 
 // Timer is the interface for emitting timer metrics.