# valtype::creditcard::amex(3tcl) 1 valtype "Validation types"

## Name

valtype::creditcard::amex - Validation for AMEX creditcard number

## Synopsis

- package require Tcl 8.5
- package require snit 2
- package require valtype::common
- package require valtype::luhn
- package require valtype::creditcard::amex ?1?

- valtype::creditcard::amex validate value
- valtype::creditcard::amex checkdigit value

## Description

This package implements a snit validation type for an AMEX creditcard number.

A validation type is an object that can be used to validate Tcl values of a particular kind. For example, snit::integer, a validation type defined by the snit package is used to validate that a Tcl value is an integer.

Every validation type has a validate method which is used to do the validation. This method must take a single argument, the value to be validated; further, it must do nothing if the value is valid, but throw an error if the value is invalid:

        valtype::creditcard::amex validate .... ;# Does nothing
        valtype::creditcard::amex validate .... ;# Throws an error (bad American Expresss creditcard number).

The validate method will always return the validated value on success, and throw the -errorcode INVALID on error, possibly with additional elements which provide more details about the problem.

## API

The API provided by this package satisfies the specification of snit validation types found in the documentation of Snit's Not Incr Tcl.

valtype::creditcard::amex validate value

  This method validates the value and returns it, possibly in a canonical form, if it passes. If the value does not pass the validation an error is thrown.

valtype::creditcard::amex checkdigit value

  This method computes a check digit for the value. Before doing so it is validated, except for a checkdigit. If the value does not pass the validation no check digit is calculated and an error is thrown instead.

## Error Codes

As said in the package description, the errors thrown by the commands of this package in response to input validation failures use the -errorcode INVALID to distinguish themselves from package internal errors.

To provide more detailed information about why the validation failed the -errorCode goes actually beyond that. First, it will contain a code detailing the type itself. Here this is CREDITCARD AMEX. This is then followed by values detailing the reason for the failure. The full set of -errorCodes which can be thrown by this package are:

INVALID CREDITCARD AMEX CHARACTER

  The input value contained one or more bad characters, i.e. characters which must not occur in the input for it to be an AMEX creditcard number.

INVALID CREDITCARD AMEX CHECK-DIGIT

  The check digit of the input value is wrong. This usually signals a data-entry error, with digits transposed, forgotten, etc. Of course, th input may be an outright fake too.

INVALID CREDITCARD AMEX LENGTH

  The input value is of the wrong length to be an AMEX creditcard number.

INVALID CREDITCARD AMEX PREFIX

  The input value does not start with the magic value(s) required for it to be an AMEX creditcard number.

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category valtype of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

When proposing code changes, please provide unified diffs, i.e the output of diff -u.

Note further that attachments are strongly preferred over inlined patches. Attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar.

## Keywords

AMEX, American Express, Checking, Testing, Type checking, Validation, Value checking, bank, card for credit, credit card, finance, isA

## Category

Validation, Type checking

## Copyright

Copyright © 2011 Andreas Kupries <andreas_kupries@users.sourceforge.net>