Use must_use on the ObserveWhen

Otherwise, nothing would get observed, so better warn on it.
2019-07-11 18:39:51 +02:00 · 2019-07-11 18:39:51 +02:00 · ea96d5c6a0
parent 3147ca034f
commit ea96d5c6a0
1 changed files with 1 additions and 0 deletions
--- a/src/core/attributes.rs
+++ b/src/core/attributes.rs
@ -197,6 +197,7 @@ pub trait Observe {
    /// common.
    type Inner;
    /// Provide a source for a metric's values.
+    #[must_use = "must specify when to observe"]
    fn observe<F>(
        &self,
        metric: impl Deref<Target = InputMetric>,