get(::Function, ::Dict, ::Key) not defined for Base.ImmutableDict?

General Usage
1

While playing around with Dicts, I found that I was not able to use the do-block syntax, e.g.

get(a, key) do
    @warn "Key not found. Falling back to default"
    default
end

when a is of type Base.ImmutableDict instead of Dict. Is there a reason it isn’t implemented, and is there a workaround I can use instead? (I guess I could make a custom version of the function by looking at dict.jl on GitHub though I’m not sure that’s the best idea)

2

Seems like an oversight (a missing fallback method for AbstractDict), since the documentation lists get(f::Function, collection, key) as a generic method for any collection. Maybe file an issue?

As a workaround, you could define something like

struct _KeyNotFound; end
function myget(default::Base.Callable, collection, key)
    result = get(collection, key, _KeyNotFound())
    return result isa _KeyNotFound ? default() : result
end
2 Likes
3

Thank you, that is a more elegant workaround than what I had come up with! I will file that as an issue as well.