1 files changed, 73 insertions, 0 deletions
diff --git a/indra/newview/scripts/lua/mapargs.lua b/indra/newview/scripts/lua/mapargs.lua
new file mode 100644
index 0000000000..45f5a9c556
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+++ b/indra/newview/scripts/lua/mapargs.lua
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+-- Allow a calling function to be passed a mix of positional arguments with
+-- keyword arguments. Reference them as fields of a table.
+-- Don't use this for a function that can accept a single table argument.
+-- mapargs() assumes that a single table argument means its caller was called
+-- with f{table constructor} syntax, and maps that table to the specified names.
+-- Usage:
+-- function f(...)
+--     local a = mapargs({'a1', 'a2', 'a3'}, ...)
+--     ... a.a1 ... etc.
+-- end
+-- f(10, 20, 30)     -- a.a1 == 10,  a.a2 == 20,  a.a3 == 30
+-- f{10, 20, 30}     -- a.a1 == 10,  a.a2 == 20,  a.a3 == 30
+-- f{a3=300, a1=100} -- a.a1 == 100, a.a2 == nil, a.a3 == 300
+-- f{1, a3=3}        -- a.a1 == 1,   a.a2 == nil, a.a3 == 3
+-- f{a3=3, 1}        -- a.a1 == 1,   a.a2 == nil, a.a3 == 3
+local function mapargs(names, ...)
+    local args = table.pack(...)
+    local posargs = {}
+    local keyargs = {}
+    -- For a mixed table, no Lua operation will reliably tell you how many
+    -- array items it contains, if there are any holes. Track that by hand.
+    -- We must be able to handle f(1, nil, 3) calls.
+    local maxpos = 0
+
+    -- For convenience, allow passing 'names' as a string 'n0,n1,...'
+    if type(names) == 'string' then
+        names = string.split(names, ',')
+    end
+
+    if not (args.n == 1 and type(args[1]) == 'table') then
+        -- If caller passes more than one argument, or if the first argument
+        -- is not a table, then it's classic positional function-call syntax:
+        -- f(first, second, etc.). In that case we need not bother teasing
+        -- apart positional from keyword arguments.
+        posargs = args
+        maxpos = args.n
+    else
+        -- Single table argument implies f{mixed} syntax.
+        -- Tease apart positional arguments from keyword arguments.
+        for k, v in pairs(args[1]) do
+            if type(k) == 'number' then
+                posargs[k] = v
+                maxpos = math.max(maxpos, k)
+            else
+                if table.find(names, k) == nil then
+                    error('unknown keyword argument ' .. tostring(k))
+                end
+                keyargs[k] = v
+            end
+        end
+    end
+
+    -- keyargs already has keyword arguments in place, just fill in positionals
+    args = keyargs
+    -- Don't exceed the number of parameter names. Loop explicitly over every
+    -- index value instead of using ipairs() so we can support holes (nils) in
+    -- posargs.
+    for i = 1, math.min(#names, maxpos) do
+        if posargs[i] ~= nil then
+            -- As in Python, make it illegal to pass an argument both positionally
+            -- and by keyword. This implementation permits func(17, first=nil), a
+            -- corner case about which I don't particularly care.
+            if args[names[i]] ~= nil then
+                error(string.format('parameter %s passed both positionally and by keyword',
+                                    tostring(names[i])))
+            end
+            args[names[i]] = posargs[i]
+        end
+    end
+    return args
+end
+
+return mapargs