func main() {
	v := viper.New()
	v.SetConfigFile("config.yml")
	v.Set("number", 100)
	v.SafeWriteConfig()
}

// In this example I suppose not writing the config doesn't surprise
// me as much because the docs of `SetConfigFile` say that all
// paths are ignored. So maybe viper doesn't know the exact path
// of the file.
v.SetConfigFile("config.yml")
v.AddConfigPath(".")
v.SafeWriteConfig()

// But in this example with the full path, I would expect viper to
// write the config there.
v.SetConfigFile(`full/path/to/config.yml`)
v.SafeWriteConfig()

v.SetConfigName("config")
v.SetConfigType("yml")
v.AddConfigPath(".")
v.SafeWriteConfig()

// Writes config to "config.yml" in the current directory (probably
// config is some default value for the name).
v.SetConfigFile("test.yml")
v.SetConfigType("yml")
v.AddConfigPath(".")
v.SafeWriteConfig()

// Writes config to "config.yml" in the current directory.
// Note that in this case viper will not read the config
// from "config.yml", if some config is there. Instead, it
// will read from "test.yml", which makes it even more
// confusing why the config is written to "config.yml".
v.SetConfigFile("config")
v.SetConfigType("yml")
v.AddConfigPath(".")

v.SetConfigFile("test.yml")
v.SafeWriteConfig()

// Writes config in current directory to "test.yml"
v.SetConfigFile("test.yml")
v.WriteConfig()

// Doesn't do anything apparently
v.SetConfigName("config")
v.SetConfigType("yaml")
v.AddConfigPath(".")
v.WriteConfig()