Simple, consistant, multi-value form behaviour

The problem with the current behaviour

At the moment, form support is a bit messy. Repeating inputs with the same name causes the last value to overwrite all the others, unless the name ends with [] in which case a list of all provided values is formed — unless you're using a multipart form, in which case multiple values with [] doesn't work at all.

I assume the [] at the end convention is taken from PHP which does this, but I find it needlessly complicates the situation. Consider the following examples:

foo=1&foo=2
foo[]=1&foo[]=2
foo[]=1&foo=2
foo=1&foo[]=2
foo=1&foo[]=2&foo=3

The first two have a semi-obvious behaviour, but beyond that, the situation … deteriorates.

It's also a bit annoying to write Symbol("name[]") instead of :name when accepting multiple values.

I think we can do better.

My proposal

I propose a breaking change for v5, to make form values be handled in a simpler, and more consistent manner.

Treat all form fields as multi-value, with no ifs, buts or ands

Consider the following example:

<form>
  <input type="text" name="foo" value="1"/>
  <input type="text" name="foo" value="2"/>
  <input type="text" name="bar" value="3"/>
</form>

Depending on whether you put [] after foo or not you'll either see

Dict{Symbol, String} with 2 entries:
  :bar => "3"
  :foo => "2"

Dict{Symbol, Union{String, Vector{String} with 2 entries:
  :bar => "3"
  Symbol("foo[]") => ["1", "2"]

By treating all form fields as multi-value, you'd have the following result

Dict{Symbol, Vector{String}} with 2 entries:
  :bar => ["3"]
  :foo => ["1", "2"]

This has a few advantages:

No information is lost by default
No more hassle with [] in the name or Symbol("...[]")
It's simpler to reason about mentally, by having a simpler model and more uniform data type
It's easy to obtain single-value behaviour with payload[:name][end]

GenieFramework / Genie.jl

Simple, consistant, multi-value form behaviour #483

The problem with the current behaviour

My proposal