# Dict's different behavior for using and include

**URL:** <https://discourse.julialang.org/t/dicts-different-behavior-for-using-and-include/47058>\
**Category:** General Usage\
**Created:** [September 22, 2020, 10:40am UTC](https://discourse.julialang.org/t/dicts-different-behavior-for-using-and-include/47058 "2020-09-22T10:40:47Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![N5N3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/n5n3/32/17663_2.png) [@N5N3](https://discourse.julialang.org/u/N5N3)\
**Post date:** [September 22, 2020, 10:40am UTC](https://discourse.julialang.org/t/dicts-different-behavior-for-using-and-include/47058/1 "2020-09-22T10:40:47Z")

</div>

First, I created a file named `DictTest.jl` with the following content:

```julia
module DictTest
data = Dict(GlobalRef(Base,:sum) => GlobalRef(Base,:prod),
    1 => GlobalRef(Base,:sum))
end

```

and put the file into the `JULIA_LOAD_PATH`.

Then in REPL:

```julia
julia> using DictTest
[Info: Precompiling DictTest [top-level]

julia> DictTest.data
Dict{Any,GlobalRef} with 2 entries:
  :(Base.sum) => :(Base.prod)
  1 => :(Base.sum)

julia> DictTest.data[1]
:(Base.sum)

julia> DictTest.data[GlobalRef(Base,:sum)]
ERROR: KeyError: key :(Base.sum) not found
Stacktrace:
 [1] getindex(::Dict{Any,GlobalRef}, ::GlobalRef) at .\dict.jl:467
 [2] top-level scope at none:1

julia> DictTest.data.keys[10]
:(Base.sum)

julia> DictTest.data[DictTest.data.keys[10]]
ERROR: KeyError: key :(Base.sum) not found
Stacktrace:
 [1] getindex(::Dict{Any,GlobalRef}, ::GlobalRef) at .\dict.jl:467
 [2] top-level scope at none:1

```

The last result make me crazy.

Restart Julia, and

```julia
julia> cd(ENV["JULIA_LOAD_PATH"][1:end-1])

julia> include("DictTest.jl")
Main.DictTest

julia> DictTest.data[1]
:(Base.sum)

julia> DictTest.data[GlobalRef(Base,:sum)]
:(Base.prod)

```

It seem `using` gives a wrong result while `include` is ok. I have little knowledge about Julia’s pre-compile, is this a feature or a bug?

Here’s the versioninfo:

```julia
Julia Version 1.5.1
Commit 697e782ab8 (2020-08-25 20:08 UTC)
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: Intel(R) Core(TM) i5-9600KF CPU @ 3.70GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-9.0.1 (ORCJIT, skylake)

```

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [September 22, 2020, 10:53am UTC](https://discourse.julialang.org/t/dicts-different-behavior-for-using-and-include/47058/2 "2020-09-22T10:53:43Z")

</div>

You probably need to `rehash!` the dictionary after precompilation since the serialized hashes are not valid anymore.

So you can add

```julia
function __init__ ()
    Base.rehash!(data)
end

```

to your module. Also, don’t use the `.keys` field for dictionaries, it’s an internal field.

Specifically, see this part in the manual [Modules · The Julia Language](https://docs.julialang.org/en/v1/manual/modules/#Module-initialization-and-precompilation:)

> Dictionary and set types, or in general anything that depends on the output of a `hash(key)` method, are a trickier case. In the common case where the keys are numbers, strings, symbols, ranges, `Expr` , or compositions of these types (via arrays, tuples, sets, pairs, etc.) they are safe to precompile. However, for a few other key types, such as `Function` or `DataType` and generic user-defined types where you haven’t defined a `hash` method, the fallback `hash` method depends on the memory address of the object (via its `objectid` ) and hence may change from run to run. If you have one of these key types, or if you aren’t sure, to be safe you can initialize this dictionary from within your ` __init__ ` function. Alternatively, you can use the [`IdDict`](https://docs.julialang.org/en/v1/base/collections/#Base.IdDict) dictionary type, which is specially handled by precompilation so that it is safe to initialize at compile-time.

So a better solution than I wrote above is likely to use an `IdDict`

---

<div class="post-metadata">

**Author:** ![N5N3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/n5n3/32/17663_2.png) [@N5N3](https://discourse.julialang.org/u/N5N3)\
**Post date:** [September 22, 2020, 10:59am UTC](https://discourse.julialang.org/t/dicts-different-behavior-for-using-and-include/47058/3 "2020-09-22T10:59:26Z")

</div>

Solved, thanks very much.