feat: can resolve another dependency

README.md

@@ -89,6 +89,16 @@ userServiceDep.injection({
 
 ---
 
+### Reference another dependency
+
+```ts
+const postServiceDep = new Dependency(
+  async (c) => new PostService(await userServiceDep.resolve(c)),
+);
+```
+
+---
+
 ### A service can also be something other than a class
 
 For example, using headers from `c.req.headers`.

src/dependency.ts

@@ -21,7 +21,10 @@ export class Dependency<Service> {
     },
   ) {}
 
+  // service cache
   private service?: Service;
+  // used as a basis for caching when evaluating the request scope
+  private lastRequest?: Request;
 
   /**
    * Injects a service instance directly. Useful for overriding the default service.
@@ -39,6 +42,21 @@ export class Dependency<Service> {
     return this;
   }
 
+  /**
+   * Resolve service.
+   */
+  async resolve(c: Context): Promise<Service> {
+    // evaluate and clear the cache when handling the request scope
+    if (this.opts?.scope === "request" && this.lastRequest !== c.req.raw) {
+      this.service = undefined;
+      this.lastRequest = c.req.raw;
+    }
+
+    const service = (this.service ??= await this.serviceInitializer(c));
+
+    return service;
+  }
+
   /**
    * Creates a middleware that injects the service into the context.
    */
@@ -51,10 +69,7 @@ export class Dependency<Service> {
     };
   }> {
     return async (c, next) => {
-      const service =
-        this.opts?.scope === "request"
-          ? await this.serviceInitializer(c)
-          : (this.service ??= await this.serviceInitializer(c));
+      const service = await this.resolve(c);
 
       c.set(contextKey, service);