Support validation before and after conversion

[t6d]

In some scenarios, it might be necessary to perform validation before performing the conversion. This is currently unsupported.

[fabrik42]

Example use case: I want to use a smart properties class to validate/handle a ISO8601 date string.

So I want smart_properties to do the following:

• Check the input, that it is a valid ISO8601 string (not implemented yet)
• Convert the string to a ruby Date object (currently converts)
• Make sure, that it is a Date object (currently accepts)

In this case, you need to check accepts before the converts - otherwise it could lead to a date parser error, in case the date string is not valid.

[benedikt]

While I understand that having this as a core feature would be nice, I can think of two other ways to implement this without the need for a core feature:

• Just raise an exception in the converter method (accepts would raise anyways)
• Let the converter return nil or something else to indicate that converting failed and check for that value in accepts

If I understand it correctly, you'd nonetheless need both a accept before and after the conversion. Just because the string has a valid format, doesn't necessarily mean that the value makes any sense (think leap years)

[fabrik42]

In my specific use case, I don't want to raise an exception. The whole point of the class would be to validate/prepare a combination of given params. If it raises, I would need another layer above the class to handle these exceptions.

I don't want the converter to return nil, because this would basically move the validation logic into the converter and I can not determine, if the input was just invalid or not given at all.

I personally think that smart_properties can become very handy for input validation - but in real world scenarios with user input, we should have one more callback before the converter to make sure the converter does not crash.

[t6d]

There is no harm in adding a prepares hook, so that the execution order would be prepares -> converts -> accepts. I'll actually try and release this as a feature to SmartProperties v1.x..

[t6d]

By the way, I can highly recommend using dedicated objects for complex validation and conversion operations: SmartProperties advanced input validation.

[fabrik42]

:+1: