$in = "in"; $out = "out"; Those are not really abstractions, just extracted variables. An abstraction would change the concept language. $suffix = "pu

$in = "in"; $out = "out"; Those are not really abstractions, just extracted variables. An abstraction would change the concept language. $suffix = "put"; This is also not an abstraction, as the language of the term "suffix" comes from its role in string concatenation, which is the same as the role of the original string literal. It doesn't change the "level of abstraction". This isn't an over-abstraction, it's an over-extraction. Each abstraction should be non-trivial. $project_folder = "/whatever"; is a good abstraction. Looking at the string literal "/whatever", I cannot determine it's "role", but $project_folder is a good name and changes the concept language from being about string concatenation or arbitrary names into a concept language about projects and folders.