As always the answer is somewhere in the middle. For a core library that your company or even better everyone using the framework as you uses everyday implicitn

As always the answer is somewhere in the middle. For a core library that your company or even better everyone using the framework as you uses everyday implicitness is great. You invest a little bit upfront and it keeps paying off everyday. For one-off code you hardly ever touch you better be explicit. Of course there trick here is knowing which one you are writing. A good rule of thumb might be you start explicit and over time add an implicit layer on top while refactoring. With DHH's Active Record example that would have worked out nicely, since from the API perspective is really just reasonable defaults that could have been added once you realize that Active Record thing is actually being used in frequently.