[Feature Request] Ability to set validator about schema

[kisielk]

I don't really see the motivation. How is it easier than just validating the value of Foo after it has been decoded?

[nvcnvn]

Yes, not much but ...some convenience...
For example you can add the error from validtaor to the MultiError list.
And then we can provide some default validator for user with some thing similar with JQuery Validator plugin etc...

P/s: It sound not as that good but when I use ASP.NET they provide something like that...and some how I miss them :D

[kisielk]

Right, so the main purpose would be so the errors show up in the MultiError list ?

[kisielk]

Also do you have a link to the docs for the ASP.NET version? Would be curious to see how theirs works.

[nvcnvn]

Yes, we can say the main purpose is "helping lazy one" 😄
In ASP.NET MVC they have some attributes for model class, you can find for "[Required]" example in this link
http://www.asp.net/mvc/tutorials/mvc-4/getting-started-with-aspnet-mvc4/adding-validation-to-the-model
(I think Go struct tags can be an alternative for Java Annotations or C# Attributes?)

[kisielk]

I definitely don't want to invent some kind of microlanguage in struct tags for validation, so I think that's out. It seems to me that giving schema the ability to register some kind of callback validator to be called upon decode isn't much better than simply calling a validation function after decoding has been completed. I'm willing to be convinced otherwise, but closing this for now.