Better error message: KeyError

[BeastyBlacksmith]

I think a low hanging fruit might be the improvement of the printing of KeyError from:

julia> Dict( :a => 1, :b => 2)[:c]
ERROR: KeyError: key :c not found
Stacktrace:
 [1] getindex(::Dict{Symbol,Int64}, ::Symbol) at ./dict.jl:477
 [2] top-level scope at none:0

To

ERROR: KeyError: key :c not found. Available keys are: (:a, :b).

[rfourquet]

Is it still useful when many keys are available and only few of them can be displayed in the error message?

[BeastyBlacksmith]

Well, the best thing would be, to pick a limited amount of "closest keys".
Still, printing any amount of keys is potentially more helpful than not printing any keys, since it might give you an idea about what dictionary didn't have that key.

[StefanKarpinski]

Keys can be arbitrary objects. How do you pick the "closest" arbitrary objects to another object?

[BeastyBlacksmith]

That can fallback to printing the first n-entries for objects that don't have a metric.
And if this is the only method then also fine, still an improvement.