extension method
Extracts the extension (without the leading dot) of self.file_name, if possible.
Implementation
String extension() {
String extensionWithDot = _posix.extension(string);
if (extensionWithDot.isNotEmpty) {
assert(extensionWithDot.startsWith("."));
return extensionWithDot.replaceFirst(".", "");
}
return extensionWithDot;
}