Iteration order of `Dict`

[3f6a]

If dict::Dict, are all of the following:

keys(dict)
values(dict)
pairs(dict)
[(k,v) for (k,v) in dict]

guaranteed to iterate entries of dict in the same order ?

Currently the documentation states that keys(dict) and values(dict) iterate in the same order. But it is not stated whether this is the same order as that used by pairs(dict), or when looping, for (k,v) in dict.

If this is guaranteed, can it be mentioned explicitly in the documentation?

[oscardssmith]

I think this would be reasonable to document/guarentee. It's somewhat hard to imagine a decent Dict design where this wouldn't be true.

[3f6a]

Where would it go ? The docs for keys, values, and pairs ?

I presume that when looping, for (k,v) in dict, this is implicitly calling pairs ?

[inkydragon]

I presume that when looping, for (k,v) in dict, this is implicitly calling pairs ?

The [for ... in] syntax and pairs both use Generator to iterate over collections.
And normal for loop use Base.iterate.

julia/base/abstractdict.jl

Lines 174 to 176 in b4c5e58

	pairs(collection) = Generator(=>, keys(collection), values(collection))
	pairs(a::AbstractDict) = a

julia> d = Dict([1=>1, 2=>2])
Dict{Int64, Int64} with 2 entries:
  2 => 2
  1 => 1

julia> f() = [ (k,v) for (k,v) in d ]
f (generic function with 1 method)

julia> @code_lowered f()
CodeInfo(
1 ─ %1 = Main.:(var"#11#12")
│        #11 = %new(%1)
│   %3 = #11
│   %4 = Main.d
│   %5 = Base.Generator(%3, %4)
│   %6 = Base.collect(%5)
└──      return %6
)

[DilumAluthge]

If it's going to be explicitly guaranteed in the documentation, there should probably be tests to make sure it doesn't regress. Do we currently have such tests?

[cossio]

Added some tests: 8c6dc4a (there were already some tests just above, but I think did not cover all cases)