Archive: October 2019

Functional dependency injection in Scala using ZIO environments

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Chiel van de Steeg

ZIO is a type-safe, composable library for asynchronous and concurrent programming in Scala (from: The ZIO github). The library copes with functional IO, like many Functional Programming libraries do. The added value of ZIO is that the ZIO[R, E, A] type-constructor (the main IO monad of the library) acts as an IO monad, an error handling monad, and a reader monad. A functional programming style often needs a combination of these three types to cope with the most common problems when creating an application:

  • performing side effects (getting the A)

  • coping with errors (handling E)

  • supplying dependencies (providing R)

This blogpost will show you how to cope with the R part of a ZIO[R, E, A]: the Environment

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Spring Security: Custom Permission Evaluator

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Tim te Beek

Often you’ll find access decisions move beyond simplistic ownership or having a certain role, for instance when users share domain objects with other users. In such cases it’s common to separate permission to view an instance from being able to make changes to the same instance. When your access rules are relatively straightforward, Spring Security offers the PermissionEvaluator interface to secure instance access.

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Distributed Tracing with Kafka Streams

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Tim te Beek

Distributed tracing is a method used to profile and monitor applications, especially those built using a microservices architecture. Distributed tracing helps pinpoint where failures occur and what causes poor performance.[1] Applied to Kafka Streams it allows us to trace and visualize our messages by propagating diagnostic information within message headers.

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Don't pass null to a function

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Ties van de Ven

I have seen the following pattern appear quite a lot:

private String foo(String bar) {
  if(bar != null){
    return "bar";
  }
  return null;
}

Here the function is called with a nullable argument, and if the argument was null, the function will return null, and if not it will return a proper value. I do not like this, and here is why.

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Converting Char to Int in Kotlin

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Riccardo Lippolis

The Kotlin standard library contains a lot of helper functions on top of the Java standard library for our convenience. Some of those functions help us in converting between different data types. For example, the String.toInt() function converts a number formatted as String to its Int representation. But how do we accomplish the same with a Char? Spoiler alert: NOT by using Char.toInt()!

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Kotlin method reference to companion object function

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Riccardo Lippolis

Functions defined in Kotlin companion objects are often seen as the 'equivalent' of static methods in Java. Although there are some similarities, there are also some caveats you should be aware of. For example, how to use method references (or, to be pedantic: function references) to refer to functions defined in a companion object.

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