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--[[
Transformer.lua
A transforming meta-flow originally built for packer.
TL;DR you have a function to which you want to eventually pass a table.
With this, you can construct the table piece by piece.
It will finally call out once you pass () or a string.
The string will *prepend* itself to the object.
Merging rules are a bit complicated:
For tables, we merge the ipairs in order (left to right).
The final '' is an exception.
Then we merge the map-like keys recursively.
If the target is a table but the merged key isn't, we append it.
Otherwise we always overwrite.
]]--
---@diagnostic disable-next-line: unused-vararg
local function tables(...)
for i=1,select('#') do
if type(select(i)) ~= 'table' then return false end
end
return true
end
local function imerge(t1, t2) -- mutates t1
for _, v in ipairs(t2) do table.insert(t1, v) end
end
local bigmerge -- forward declaration
local function kmerge(t1, t2) -- mutates t2
for k, v in pairs(t2) do
if type(k) == 'number' and k >= 1 and k <= #t1 then
-- skip, we did this in imerge
else
if t1[k] and type(t1[k]) == 'table' then
if type(v) == 'table' then
t1[k] = bigmerge(t1[k], v)
else
table.insert(t1[k], v)
end
else
t1[k] = v
end
end
end
end
bigmerge = function(t1, t2)
assert(tables(t1, t2))
local out = {}
imerge(out, t1)
imerge(out, t2)
kmerge(out, t1)
kmerge(out, t2)
return out
end
local function tgen(use) return function (self, obj)
if obj == nil then return use(self) end
if type(obj) == 'string' then
local out = { obj }
imerge(out, self)
kmerge(out, self)
return setmetatable(out, getmetatable(self))()
elseif type(obj) == 'table' then
local out = bigmerge(self, obj)
return setmetatable(out, getmetatable(self))
else
error 'Invalid argument.'
end
end end
return function(use)
return setmetatable({}, { __call = tgen(use) })
end
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