[Needs discussion] Add support for arrays

[Kangaroux]

We should support type checking arrays just like any other value.

I'm not sure what the best way of reporting type mismatches would be. The two things that come to mind would be to report the entire array as a mismatch, or to report each individual index as a mismatch.

Calling out the specific indexes that are mismatched would definitely be a bit too verbose in most cases. I'd also be willing to bet that if one of the indexes is mismatched then chances are the whole array is mismatched.

On the other hand, I'd rather be overly verbose and provide a way to simplify the mismatch reporting.

[Kangaroux]

[]int example

Struct

type MyStruct struct {
    Foo []int `json:"foo"`
}

Input

{
    "foo": [1, 2, null]
}

Could report

1. expected "foo[2]" to be an int but it's null

OR

2. expected "foo" to be an []int but one or more elements are not an int

[Kangaroux]

[]Person example v1

Struct

type Person struct {
    Name string `json:"name"`
}

type MyStruct struct {
    People []Person `json:"people"`
}

Input

{
    "people": [
        {"name": "Jessie"},
        5
    ]
}

Could report

1. expected "people[1]" to be a Person but it's an int

OR

2. expected "people" to be a []Person but one or more elements are not a Person

[Kangaroux]

The previous two examples are simple enough but there's the case that there's a deep mismatch within the array.

In this case the name field for the Person object is invalid, so we report that as being a problem. It wouldn't be helpful to simply report the entire array as invalid without giving the specific reason.

[]Person example v2

Struct

type Person struct {
    Name string `json:"name"`
}

type MyStruct struct {
    People []Person `json:"people"`
}

Input

{
    "people": [
        {"name": 123.45}
    ]
}

Could report

expected "people[0].name" to be a string but it's a float

[Kangaroux]

I think we can probably reach a good compromise if there was a mismatch type for arrays. The array mismatch type would contain the specific element mismatches, so that info is still available if you decide to report each individual element.