# Strong typed Dict{String, Int64} getindex(String) returns Any instead of Int64 value type?

**URL:** <https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856>\
**Category:** New to Julia\
**Tags:** dictionary, code\_warntype\
**Created:** [May 11, 2022, 3:43am UTC](https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856 "2022-05-11T03:43:33Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![FireCrumb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/firecrumb/32/35370_2.png) [@FireCrumb](https://discourse.julialang.org/u/FireCrumb)\
**Post date:** [May 11, 2022, 3:43am UTC](https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856/1 "2022-05-11T03:43:33Z")

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If my `Dict` has a strong type defining it’s keys and values (and indeed it doesn’t let me add a different type), then why `getindex` from said `Dict` returns unstable `Any`?

```julia
julia> mydict = Dict([("A", 1), ("B", 2)])
Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1

julia> mydictlookup(mykey) = mydict[mykey]
mydictlookup (generic function with 1 method)

julia> @code_warntype mydictlookup("A")
MethodInstance for mydictlookup(::String)
  from mydictlookup(mykey) in Main at REPL[74]:1
Arguments
  #self#::Core.Const(mydictlookup)
  mykey::String
Body::Any
1 ─ %1 = Base.getindex(Main.mydict, mykey)::Any
└── return %1

```

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<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [May 11, 2022, 4:07am UTC](https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856/2 "2022-05-11T04:07:33Z")

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It’s because `mydict` is a non-const global variable:

```julia
julia> mydict = Dict([("A", 1), ("B", 2)])
Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1

julia> mydictlookup(mykey) = mydict[mykey]
mydictlookup (generic function with 1 method)

julia> mydictlookup("A")
1

julia> mydict = [1, 2]
2-element Vector{Int64}:
 1
 2

julia> mydictlookup("A")
ERROR: ArgumentError: invalid index: "A" of type String
Stacktrace:
 [1] to_index(i::String)
   @ Base ./indices.jl:300
 [2] to_index(A::Vector{Int64}, i::String)
   @ Base ./indices.jl:277
 [3] to_indices
   @ ./indices.jl:333 [inlined]
 [4] to_indices
   @ ./indices.jl:325 [inlined]
 [5] getindex(A::Vector{Int64}, I::String)
   @ Base ./abstractarray.jl:1170
 [6] mydictlookup(mykey::String)
   @ Main ./REPL[2]:1
 [7] top-level scope
   @ REPL[5]:1

julia> mydictlookup(1)
1

```

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<div class="post-metadata">

**Author:** ![FireCrumb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/firecrumb/32/35370_2.png) [@FireCrumb](https://discourse.julialang.org/u/FireCrumb)\
**Post date:** [May 11, 2022, 4:24am UTC](https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856/3 "2022-05-11T04:24:03Z")

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> [@odow](#):
>
> It’s because `mydict` is a non-const global variable:
> 
> ```julia
> 
> ```

Ah so `const` was making all the difference!

```julia
julia> const mydict2 = Dict([("A", 1), ("B", 2)])
Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1

julia> mydict2lookup(mykey) = mydict2[mykey]
mydict2lookup (generic function with 1 method)

julia> mydict2lookup("A")
1

julia> @code_warntype mydict2lookup("A")
MethodInstance for mydict2lookup(::String)
  from mydict2lookup(mykey) in Main at REPL[80]:1
Arguments
  #self#::Core.Const(mydict2lookup)
  mykey::String
Body::Int64
1 ─ %1 = Base.getindex(Main.mydict2, mykey)::Int64
└── return %1

```

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<div class="post-metadata">

**Author:** ![Jeff\_Emanuel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeff_emanuel/32/15440_2.png) [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)\
**Post date:** [May 11, 2022, 2:10pm UTC](https://discourse.julialang.org/t/strong-typed-dict-string-int64-getindex-string-returns-any-instead-of-int64-value-type/80856/4 "2022-05-11T14:10:40Z")

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> [@FireCrumb](#):
>
> Ah so `const` was making all the difference!

[https://docs.julialang.org/en/v1/manual/performance-tips/](https://docs.julialang.org/en/v1/manual/performance-tips/)