Feature request: adding common fault Error into standard lib

[alexveden]

I found that I need to implement custom error type for some common cases like index error, or collection overflow, or bad argument myself. Maybe it would be more convenient to have something common in standard lib?

The main idea is to make vague error classes, for example: for a function which opens a file by path it could fail when file not found, file name is a directory, permission violation, or IO error while reading. And the caller code might not handle all tiny variations of error cases, it just wishes to know that the operation failed. So for this case, it could be useful to have a set of general purpose errors in the stdlib.

This proposal for the cases when the operation is insignificant, or error cases are too generic to make a special fail MyError class for this.

Here are some ideas of common errors:

1. Argument error - parameter of a function didn't pass sanity check, this could be applicable to console args parsing too.
2. Memory error - out of memory.
3. Overflow error - buffer overflow, number overflow, math overflow.
4. NotFound error - something is not existing, missing stuff
5. Index error - array, data, index error or out of bounds
6. Already exists - something what you are trying to make is already exists
7. KeyError - key is not found or adding same key name
8. ValueError - value of the thing is bad, or maybe math operation error.
9. OS Error / System Error - OS API or general error
10. IO error - general IO error
11. Stop Iterator error - for supporting non-bound iterators while(try item = iterator.next()) stopping
12. Runtime error - some general purpose error

Some more specific but also useful:

1. Connection error - DB, network, device connection error
2. Timeout - timer timeout, socket timeout, etc.
3. Access/Permission error - file, resource, device access error