# How can I use \`get\` with a subtype of a Dict key?

**URL:** <https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857>\
**Category:** General Usage\
**Created:** [January 12, 2023, 9:38am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857 "2023-01-12T09:38:28Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![gleyland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gleyland/32/15339_2.png) [@gleyland](https://discourse.julialang.org/u/gleyland)\
**Post date:** [January 12, 2023, 9:38am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857/1 "2023-01-12T09:38:28Z")

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I would like to define a `Dict{A, Bool}` and then put entries with keys of type `B` (a subtype of `A`) into it. Adding `B` entries to the `Dict` works, as does indexing the `Dict` with `[]`, but `get` doesn’t seem to work:

```julia
julia> VERSION
v"1.8.2"

julia> abstract type A end; struct B <: A name end

julia> b = B("b")
B("b")

julia> d = Dict{A, Bool}(b => true)
Dict{A, Bool} with 1 entry:
  B("b") => 1

julia> d[b]
true

julia> get(d, b)
ERROR: MethodError: no method matching get(::Dict{A, Bool}, ::B)
Closest candidates are:
  get(::Dict{K, V}, ::Any, ::Any) where {K, V} at dict.jl:523
  get(::IOContext, ::Any, ::Any) at show.jl:343
  get(::WeakKeyDict{K}, ::Any, ::Any) where K at weakkeydict.jl:142
  ...

```

`get(d, convert(A, b))` doesn’t seem to work either. Is there a way to make `get` work in this case?

Thanks!

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<div class="post-metadata">

**Author:** ![skleinbo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/skleinbo/32/36080_2.png) [@skleinbo](https://discourse.julialang.org/u/skleinbo)\
**Post date:** [January 12, 2023, 9:40am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857/2 "2023-01-12T09:40:53Z")

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You are missing the third argument to `get`

```julia
help?> get
search: get get! getpid getkey getfield getindex getproperty gethostname get_zero_subnormals SegmentationFault mergewith mergewith! RegexMatch

  get(collection, key, default)

  Return the value stored for the given key, or the given default value if no mapping for the key is present.

  │ Julia 1.7
  │
  │ For tuples and numbers, this function requires at least Julia 1.7.

  Examples
  ≡≡≡≡≡≡≡≡≡≡

  julia> d = Dict("a"=>1, "b"=>2);

  julia> get(d, "a", 3)
  1

  julia> get(d, "c", 3)
  3

```

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<div class="post-metadata">

**Author:** ![gleyland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gleyland/32/15339_2.png) [@gleyland](https://discourse.julialang.org/u/gleyland)\
**Post date:** [January 12, 2023, 9:45am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857/3 "2023-01-12T09:45:46Z")

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Oh, D’oh! Thanks!

I thought there was a two argument `get` (though obviously I’ve never used it).

I’m using `get` because I can’t work out how to broadcast `[]`: `d.[[b, c]]` doesn’t work so I resorted to `get.(Ref(d), [b, c])`. `get.(Ref(d), [b, c], nothing)` works, I just never use the nothing.

Thanks!

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<div class="post-metadata">

**Author:** ![sijo](https://avatars.discourse-cdn.com/v4/letter/s/da6949/32.png) [@sijo](https://discourse.julialang.org/u/sijo)\
**Post date:** [January 12, 2023, 9:47am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857/4 "2023-01-12T09:47:08Z")

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You can use `getindex` instead of `[]`.

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<div class="post-metadata">

**Author:** ![gleyland](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gleyland/32/15339_2.png) [@gleyland](https://discourse.julialang.org/u/gleyland)\
**Post date:** [January 12, 2023, 9:48am UTC](https://discourse.julialang.org/t/how-can-i-use-get-with-a-subtype-of-a-dict-key/92857/5 "2023-01-12T09:48:12Z")

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Perfect! Thanks.