Implement dict to receive Object as key, not only String

[HyeockJinKim]

gpython/py/dict.go

Line 68 in 33327c5

type StringDict map[string]Object

Change the dict to receive a hashable object as a key, not just a string.
I will change it so that the object can be looked up through the hash value of the object.

Store the object in the slice and use the map to find the index of the stored object through the hash value.

make([]Object, 0, len(default_size))  // slice to store object  (index -> Object)
type Dict map[HashIndex]int // map to store index of slice  (Hash -> index)

Is it ok to implement dict this way?

[corona10]

@HyeockJinKim
I 'd like to recommend to implement dict by wrapping the map throw using the delegate pattern.

type Dict struct {
...
}

func (d *Dict) Put(...) (Object, error) {
...
}

func (d *Dict) Get(...) (Object, error) {
...
}

cc @ncw

[corona10]

cc @sbinet

[sbinet]

if I am not mistaken, CPython dicts are not ordered (there's collections.OrderedDict for that.)

so, couldn't we just use map[Object]Object at the core of this data structure?

[corona10]

@sbinet
FYI

Changed in version 3.7: Dictionary order is guaranteed to be insertion order. This behavior was an implementation detail of CPython from 3.6.

He might want to implement this feature.
It is okay that we decide to broken 3.4 compatibilities.
(#74 (comment))

[corona10]

@HyeockJinKim
However, as @sbinet commented.
I'd like to recommend you implement unordered key dictionary as the 1st milestone.
That will be enough for the 1st step.

cc @ncw @sbinet

[sbinet]

I stand corrected :)

ok, then what about:

type Dict struct {
    keys map[Object]int // key to index into slice of vals
    vals []Object       // values associated with the above keys
}

(I think we can rely on Go's map hashing mechanism)

[sbinet]

and if we want to retain insertion order:

type Dict struct {
    keys  map[Object]int
    items [][2]Object // key-value pair
}

[ashermancinelli]

Does anyone have a fork for this issue? Would be willing to give it a shot.

[corona10]

@ashermancinelli please ping to @HyeockJinKim
He might work on this issue :)

[HyeockJinKim]

I'm working on this issue right now.
I will work quickly and PR.