Sure, so call your reader `file` or `network` or `stream`. Don't call it `r`. Nobody is charging you by the character.
It isn't a huge deal when the code is simple, e.g. you create a reader named `r` and in the next line you use it. That's easy to understand. The problem is that the pattern propagates. A few more lines of code are added, the reader is still named `r`. It's name `r` here, so we start putting it in a struct as `r`. Soon enough the codebase is littered with instances of `r`. Not great.
It isn't a huge deal when the code is simple, e.g. you create a reader named `r` and in the next line you use it. That's easy to understand. The problem is that the pattern propagates. A few more lines of code are added, the reader is still named `r`. It's name `r` here, so we start putting it in a struct as `r`. Soon enough the codebase is littered with instances of `r`. Not great.