add get methods for cross-key-type support on Object

Completes String/Symbol interoperability for Object by adding get
methods that accept cross-key-types:

- get(f::Callable, obj::Object{String}, key::Symbol)
- get(f::Callable, obj::Object{Symbol}, key::String)
- get(obj::Object{String}, key::Symbol, default)
- get(obj::Object{Symbol}, key::String, default)

This follows up on #421 which added setindex!, delete!, and haskey
for cross-key-types.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: quinnj

src/object.jl

@@ -136,6 +136,8 @@ function Base.get(f::Base.Callable, obj::Object{K,V}, key) where {K,V}
     node !== nothing && return _v(node)::V
     return f()
 end
+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.getindex(obj::Object, key) = get(() -> throw(KeyError(key)), obj, key)
 Base.getindex(obj::Object{String}, key::Symbol) = get(() -> throw(KeyError(key)), obj, String(key))
@@ -145,6 +147,8 @@ Base.setindex!(obj::Object{Symbol}, value, key::String) = setindex!(obj, value,
 Base.delete!(obj::Object{String}, key::Symbol) = delete!(obj, String(key))
 Base.delete!(obj::Object{Symbol}, key::String) = delete!(obj, Symbol(key))
 Base.get(obj::Object, key, default) = get(() -> default, obj, 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)
 
 # support getproperty for dot access
 Base.getproperty(obj::Object{Symbol}, sym::Symbol) = getindex(obj, sym)

test/object.jl

@@ -279,7 +279,14 @@ using JSON, Test
         delete!(obj, :symbol_test)
         @test !haskey(obj, :symbol_test)
         @test !haskey(obj, "symbol_test")
-        
+
+        # Test get with Symbol key (should convert to String)
+        obj["get_test"] = "got it"
+        @test get(obj, :get_test, "default") == "got it"
+        @test get(obj, :nonexistent, "default") == "default"
+        @test get(() -> "fallback", obj, :get_test) == "got it"
+        @test get(() -> "fallback", obj, :nonexistent) == "fallback"
+
         # Test with empty object
         empty_obj = JSON.Object{String, Any}()
         @test !haskey(empty_obj, :anything)
@@ -319,6 +326,13 @@ using JSON, Test
         @test !haskey(obj, :symbol_test)
         @test !haskey(obj, "symbol_test")
 
+        # Test get with String key (should convert to Symbol)
+        obj[:get_test] = "got it"
+        @test get(obj, "get_test", "default") == "got it"
+        @test get(obj, "nonexistent", "default") == "default"
+        @test get(() -> "fallback", obj, "get_test") == "got it"
+        @test get(() -> "fallback", obj, "nonexistent") == "fallback"
+
         # Test with empty object
         empty_obj = JSON.Object{Symbol, Any}()
         @test !haskey(empty_obj, :anything)