function fieldoffset()

in src/write.jl [656:719]
60 lines of code
8 McCabe index (conditional complexity)

function fieldoffset(b, name, col)
    nameoff = FlatBuffers.createstring!(b, string(name))
    T = eltype(col)
    nullable = T >: Missing
    
    if getmetadata(col) !== nothing
        kvs = getmetadata(col)
        kvoffs = Vector{FlatBuffers.UOffsetT}(undef, length(kvs))
        for (i, (k, v)) in enumerate(kvs)
            koff = FlatBuffers.createstring!(b, String(k))
            voff = FlatBuffers.createstring!(b, String(v))
            Meta.keyValueStart(b)
            Meta.keyValueAddKey(b, koff)
            Meta.keyValueAddValue(b, voff)
            kvoffs[i] = Meta.keyValueEnd(b)
        end
        Meta.fieldStartCustomMetadataVector(b, length(kvs))
        for off in Iterators.reverse(kvoffs)
            FlatBuffers.prependoffset!(b, off)
        end
        meta = FlatBuffers.endvector!(b, length(kvs))
    else
        meta = FlatBuffers.UOffsetT(0)
    end
    
    if isdictencoded(col)
        encodingtype = indtype(col)
        IT, inttype, _ = arrowtype(b, encodingtype)
        Meta.dictionaryEncodingStart(b)
        Meta.dictionaryEncodingAddId(b, Int64(getid(col)))
        Meta.dictionaryEncodingAddIndexType(b, inttype)
        
        Meta.dictionaryEncodingAddIsOrdered(b, false)
        dict = Meta.dictionaryEncodingEnd(b)
    else
        dict = FlatBuffers.UOffsetT(0)
    end
    type, typeoff, children = arrowtype(b, col)
    if children !== nothing
        Meta.fieldStartChildrenVector(b, length(children))
        for off in Iterators.reverse(children)
            FlatBuffers.prependoffset!(b, off)
        end
        children = FlatBuffers.endvector!(b, length(children))
    else
        Meta.fieldStartChildrenVector(b, 0)
        children = FlatBuffers.endvector!(b, 0)
    end
    
    if isdictencoded(col)
        @debug "building field: name = $name, nullable = $nullable, T = $T, type = $type, inttype = $IT, dictionary id = $(getid(col))"
    else
        @debug "building field: name = $name, nullable = $nullable, T = $T, type = $type"
    end
    Meta.fieldStart(b)
    Meta.fieldAddName(b, nameoff)
    Meta.fieldAddNullable(b, nullable)
    Meta.fieldAddTypeType(b, type)
    Meta.fieldAddType(b, typeoff)
    Meta.fieldAddDictionary(b, dict)
    Meta.fieldAddChildren(b, children)
    Meta.fieldAddCustomMetadata(b, meta)
    return Meta.fieldEnd(b)
end