snapshot of https://github.com/uber-go/guide.git (master, 2026-09-15; blobs > 131072B omitted)

src/global-mut.md

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+# Avoid Mutable Globals
+
+Avoid mutating global variables, instead opting for dependency injection.
+This applies to function pointers as well as other kinds of values.
+
+<table>
+<thead><tr><th>Bad</th><th>Good</th></tr></thead>
+<tbody>
+<tr><td>
+
+```go
+// sign.go
+
+var _timeNow = time.Now
+
+func sign(msg string) string {
+  now := _timeNow()
+  return signWithTime(msg, now)
+}
+```
+
+</td><td>
+
+```go
+// sign.go
+
+type signer struct {
+  now func() time.Time
+}
+
+func newSigner() *signer {
+  return &signer{
+    now: time.Now,
+  }
+}
+
+func (s *signer) Sign(msg string) string {
+  now := s.now()
+  return signWithTime(msg, now)
+}
+```
+
+</td></tr>
+<tr><td>
+
+```go
+// sign_test.go
+
+func TestSign(t *testing.T) {
+  oldTimeNow := _timeNow
+  _timeNow = func() time.Time {
+    return someFixedTime
+  }
+  defer func() { _timeNow = oldTimeNow }()
+
+  assert.Equal(t, want, sign(give))
+}
+```
+
+</td><td>
+
+```go
+// sign_test.go
+
+func TestSigner(t *testing.T) {
+  s := newSigner()
+  s.now = func() time.Time {
+    return someFixedTime
+  }
+
+  assert.Equal(t, want, s.Sign(give))
+}
+```
+
+</td></tr>
+</tbody></table>