I caught a problem with slice values that have commas in them. The line is divided by commas, and instead of one value in a slice, you get several values. This happens with both JSON and TOML.

type Config struct {
  Section struct {
    ID []string
  }
}

{"section": {"id": ["a","b", "c,d"]}}

[section]
id = ["a", "b", "c,d"]

Result slice of Config.Section.ID will have 4 values: "a", "b", "c" and "d".

The problem is related to the way values in slices are filled. *Loader.setSlice accepts a string formed with a comma separator. I suggest using a more complex separator so that the chance of encountering it in a row is lower. For example: ",;:|".