Merge pull request #2416 from secondlife/lua-lazymod

Allow UI to have lazily-loaded submodules.

1 files changed, 55 insertions, 10 deletions

diff --git a/indra/newview/scripts/lua/require/util.lua b/indra/newview/scripts/lua/require/util.lua
index bfbfc8637c..40737a159a 100644
--- a/indra/newview/scripts/lua/require/util.lua
+++ b/indra/newview/scripts/lua/require/util.lua
@@ -15,16 +15,9 @@ local util = {}
 -- util.classctor(MyClass, MyClass.construct)
 -- return MyClass
 function util.classctor(class, ctor)
-    -- get the metatable for the passed class
-    local mt = getmetatable(class)
-    if mt == nil then
-        -- if it doesn't already have a metatable, then create one
-        mt = {}
-        setmetatable(class, mt)
-    end
-    -- now that class has a metatable, set its __call method to the specified
-    -- constructor method (class.new if not specified)
-    mt.__call = ctor or class.new
+    -- set class's __call metamethod to the specified constructor function
+    -- (class.new if not specified)
+    util.setmetamethods{class, __call=(ctor or class.new)}
 end
 
 -- check if array-like table contains certain value
@@ -66,4 +59,56 @@ function util.equal(t1, t2)
     return util.empty(temp)
 end
 
+-- Find or create the metatable for a specified table (a new empty table if
+-- omitted), and to that metatable assign the specified keys.
+-- Setting multiple keys at once is more efficient than a function to set only
+-- one at a time, e.g. setametamethod().
+-- t = util.setmetamethods{__index=readfunc, __len=lenfunc}
+-- returns a new table with specified metamethods __index, __len
+-- util.setmetamethods{t, __call=action}
+-- finds or creates the metatable for existing table t and sets __call
+-- util.setmetamethods{table=t, __call=action}
+-- same as util.setmetamethods{t, __call=action}
+function util.setmetamethods(specs)
+    -- first determine the target table
+    assert(not (specs.table and specs[1]),
+           "Pass setmetamethods table either as positional or table=, not both")
+    local t = specs.table or specs[1] or {}
+    -- remove both ways of specifying table, leaving only the metamethods
+    specs.table = nil
+    specs[1] = nil
+    local mt = getmetatable(t)
+    if not mt then
+        -- t doesn't already have a metatable: just set specs
+        setmetatable(t, specs)
+    else
+        -- t already has a metatable: copy specs into it
+        local key, value
+        for key, value in pairs(specs) do
+            mt[key] = value
+        end
+    end
+    -- having set or enriched t's metatable, return t
+    return t
+end
+
+-- On the passed module (i.e. table), set an __index metamethod such that
+-- referencing module.submodule lazily requires(path/submodule).
+-- The loaded submodule is cached in the module table so it need not be passed
+-- to require() again.
+-- 'path', like any require() string, can be relative to LuaRequirePath.
+-- Returns the enriched module, permitting e.g.
+-- mymod = util.submoduledir({}, 'mymod')
+function util.submoduledir(module, path)
+    return util.setmetamethods{
+        module,
+        __index=function(t, key)
+            local mod = require(`{path}/{key}`)
+            -- cache the submodule
+            t[key] = mod
+            return mod
+        end
+    }
+end
+
 return util