"When you work with Spring for a while, you get used to certain errors showing up only at runtime. A missing bean here, a wrong qualifier there, sometimes subtle, sometimes catastrophic. As a Java developer moving into Scala, one of the biggest surprises is: Scala prevents many of these bugs at compile time. In this article, we'll go through real Spring failure modes,"
"If you forget to declare a PaymentService bean: // No @Service or @Bean for PaymentService When you start the application, Spring throws: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'PaymentService' available The error only shows up when the app runs Scala's Approach In Scala, missing dependencies are caught by the compiler: class OrderService(using PaymentService): def placeOrder(amount: Double): Unit = summon[PaymentService].process(amount) If there's no given PaymentService in scope, your code won't compile: could not find implicit value for parameter paymentService: PaymentService No surprises at runtime."
Spring commonly surfaces missing-bean and wrong-qualifier errors only at runtime, producing exceptions like NoSuchBeanDefinitionException and qualifier mismatches. Missing beans occur when required components are not declared, and multiple beans of the same type can lead to ambiguous injections without proper qualifiers. Scala's dependency injection model uses explicit, compile-time given/using parameters and summons, so absent or conflicting dependencies fail compilation rather than runtime execution. Example Scala signatures force the presence of PaymentService in scope or yield a compile error. Compile-time wiring reduces runtime surprises, simplifies debugging, and improves reliability across modular systems.
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