gear/meta.lua

--- Functions dealing with metatables and tables merging.
--
-- @module gear.meta
-- @copyright 2022 The DoubleFourteen Code Forge
-- @author Lorenzo Cogotti

local meta = {}


--- Test whether 'obj' is an instance of a given class 'cls'.
function meta.isinstance(obj, cls)
    repeat
        local m = getmetatable(obj)
        if m == cls then return true end

        obj = m
    until obj == nil

    return false
end

--- Merge table 'from' into table 'to'.
--
-- For every field in 'from', copy it to destination
-- table 'to', whenever the same field is nil in that table.
--
-- The same process is applied recursively to sub-tables.
function meta.mergetable(to, from)
    for k,v in pairs(from) do
        if to[k] == nil then
            to[k] = type(v) == 'table' and meta.mergetable({}, v) or v
        end
    end

    return to
end

return meta