use a struct as a key for the context

Author: marten-seemann

Diff for: .travis.yml

@@ -4,13 +4,12 @@ os:
 language: go
 
 go:
-  - 1.11.x
+  - 1.15.x
 
 env:
   global:
     - GOTFLAGS="-race"
   matrix:
-    - BUILD_DEPTYPE=gx
     - BUILD_DEPTYPE=gomod
 
 

Diff for: context.go

@@ -2,7 +2,9 @@ package metrics
 
 import "context"
 
-const CtxScopeKey = "ipfs.metrics.scope"
+type ctxScopeKey struct{}
+
+var CtxScopeKey = ctxScopeKey{}
 
 func CtxGetScope(ctx context.Context) string {
 	s := ctx.Value(CtxScopeKey)