feat: Allow users to use &XxxBuilder (#148)

Signed-off-by: Xuanwo <github@xuanwo.io>

backon/src/backoff/api.rs

@@ -27,13 +27,22 @@ impl<B: Backoff> BackoffBuilder for B {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::{ConstantBuilder, ExponentialBuilder, FibonacciBuilder};
 
     fn test_fn_builder(b: impl BackoffBuilder) {
         let _ = b.build();
     }
 
     #[test]
     fn test_backoff_builder() {
-        test_fn_builder([Duration::from_secs(1)].into_iter())
+        test_fn_builder([Duration::from_secs(1)].into_iter());
+
+        // Just for test if user can keep using &XxxBuilder.
+        #[allow(clippy::needless_borrows_for_generic_args)]
+        {
+            test_fn_builder(&ConstantBuilder::default());
+            test_fn_builder(&FibonacciBuilder::default());
+            test_fn_builder(&ExponentialBuilder::default());
+        }
     }
 }

backon/src/backoff/constant.rs

@@ -84,6 +84,14 @@ impl BackoffBuilder for ConstantBuilder {
     }
 }
 
+impl BackoffBuilder for &ConstantBuilder {
+    type Backoff = ConstantBackoff;
+
+    fn build(self) -> Self::Backoff {
+        (*self).build()
+    }
+}
+
 /// ConstantBackoff offers a consistent delay with a limited number of retries.
 ///
 /// This backoff strategy is constructed by [`ConstantBuilder`].

backon/src/backoff/exponential.rs

@@ -117,6 +117,14 @@ impl BackoffBuilder for ExponentialBuilder {
     }
 }
 
+impl BackoffBuilder for &ExponentialBuilder {
+    type Backoff = ExponentialBackoff;
+
+    fn build(self) -> Self::Backoff {
+        (*self).build()
+    }
+}
+
 /// ExponentialBackoff provides a delay with exponential retries.
 ///
 /// This backoff strategy is constructed by [`ExponentialBuilder`].

backon/src/backoff/fibonacci.rs

@@ -101,6 +101,14 @@ impl BackoffBuilder for FibonacciBuilder {
     }
 }
 
+impl BackoffBuilder for &FibonacciBuilder {
+    type Backoff = FibonacciBackoff;
+
+    fn build(self) -> Self::Backoff {
+        (*self).build()
+    }
+}
+
 /// FibonacciBackoff offers a delay with Fibonacci-based retries.
 ///
 /// This backoff strategy is constructed by [`FibonacciBuilder`].