support both String and Symbol keys for all dict-operations on Objects

[hhaensel]

• add methods for setindex!(), delete!() for obj::Object{String}, key::Symbol and vice versa
• add method haskey(obj::Object{String}, key::Symbol)
• add respective tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.23%. Comparing base (928a3cc) to head (06ad3ee).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #421      +/-   ##
==========================================
+ Coverage   90.05%   90.23%   +0.18%     
==========================================
  Files           7        7              
  Lines        1347     1352       +5     
==========================================
+ Hits         1213     1220       +7     
+ Misses        134      132       -2     

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[hhaensel]

Background:
I have a program where I check for the existence of a key and if it exists, I modify the entry under certain conditions.
With the current implementation in JSON a key might exist, but I'm not allowed to modify the respective entry. Same story with deletion of entries. That's confusing.

julia> obj = JSON.parse("""{"a": "a"}""");

julia> haskey(obj, :a)
true

julia> obj[:a] = "b"
ERROR: MethodError: no method matching setindex!(::JSON.Object{String, Any}, ::String, ::Symbol)
The function `setindex!` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  setindex!(::AbstractDict, ::Any, ::Any, ::Any, ::Any...)
   @ Base abstractdict.jl:560
  setindex!(::JSON.Object{K, V}, ::Any, ::K) where {K, V}
   @ JSON ~/.julia/dev/JSON/src/object.jl:160

This PR solves that issue.

[hhaensel]

BTW, @quinnj, are you planning a new release?

[quinnj]

Thanks for the PR! This is a good follow-up to #420 for consistency.

Review Summary

Implementation: Clean and follows the existing pattern - simple delegation with key conversion. No issues here.

Tests: Comprehensive coverage for the methods added. The tests properly check both directions (Object{String} with Symbol keys and Object{Symbol} with String keys).

One Gap Remaining

After this PR, there's still one set of methods missing for full consistency - the get methods:

julia> obj = JSON.parse("""{"a": 1}""")
julia> get(obj, :a, 0)  # fails
ERROR: MethodError: no method matching find_node_by_key(::JSON.Object{String, Any}, ::Symbol)

julia> get(() -> 0, obj, :a)  # also fails
ERROR: MethodError: ...

To complete the String/Symbol interoperability, we'd also need:

Base.get(f::Base.Callable, obj::Object{String}, key::Symbol) = get(f, obj, String(key))
Base.get(f::Base.Callable, obj::Object{Symbol}, key::String) = get(f, obj, Symbol(key))
Base.get(obj::Object{String}, key::Symbol, default) = get(obj, String(key), default)
Base.get(obj::Object{Symbol}, key::String, default) = get(obj, Symbol(key), default)

Suggestion: Either add these to this PR, or we can merge this as-is and follow up with another PR. The current changes are valuable on their own.

Summary Table (after this PR)

Method	Object{String} + Symbol	Object{Symbol} + String
getindex	✅ #420	✅ #420
setindex!	✅ this PR	✅ this PR
delete!	✅ this PR	✅ this PR
haskey	✅ existing	✅ this PR
get(callable, ...)	❌ missing	❌ missing
get(..., default)	❌ missing	❌ missing

Overall this looks good to merge as-is, with an optional follow-up for the get methods.

[quinnj]

Looks good! Merging now. I'll follow up with the missing get methods in a separate commit.

[hhaensel]

@quinnj May I ask when you plan the next release?
I have a pending decision in one of my projects that depends on the implementation of this PR. I could wait or work around.