我想出了6种实现目标的技巧。本文底部列出了它们的性能基准,以评估速度。最快的技术需要在代码中区分局部变量和沙盒变量。
local SANDBOX = {
w=1920,
h=1080,
round=function(n) return math.floor(n+0.5) end
}
local CODE = "round(10*w/h) + @a * @b"
function compile(code, sandbox)
local munged = 'local _el=... return '..code:gsub('@', '_el.')
return load(munged, nil, nil, sandbox)
end
local f = compile(CODE, SANDBOX)
print(f{a=1, b=2})
print(f{a=3, b=4})
如果您不想区分更改的变量和沙盒中的变量,或者不想使用像上面那样脆弱的
sub()
函数,下一个最快的方法是改变本地变量的
__index
,然后将其作为环境传递。您可以将此包装在助手函数中,以使其更容易:
local CODE = "round(10*w/h) + a * b"
function compile(code, sandbox)
local meta = {__index=sandbox}
return {meta=meta, f=load('_ENV=... return '..code)}
end
function eval(block, locals)
return block.f(setmetatable(locals, block.meta))
end
local f = compile(CODE, SANDBOX)
print(eval(f, {a=1, b=2}))
print(eval(f, {a=3, b=4}))
以下是所有技术的基准测试结果。请注意,最快的技术可能会更快,因为与所有其他技术不同,编译函数返回一个可以直接调用的函数,而不是包装在评估辅助脚本中:
scope as a table, 2 : 0.9s (0.22µs per eval)
scope as a table : 1.1s (0.27µs per eval)
Use __ENV, change scope meta : 1.3s (0.32µs per eval)
blank env, change meta of scope : 1.6s (0.41µs per eval)
copy values over environment : 2.8s (0.70µs per eval)
setfenv, change scope meta : 3.0s (0.74µs per eval)
local SANDBOX = {
w = 1920,
h = 1080,
round = function(n) return math.floor(n+0.5) end
}
local TESTS = {
{env={a=1, b=2}, expected=18+2},
{env={a=4, b=3}, expected=18+12},
{env={a=9, b=7}, expected=18+63},
{env={a=4, b=5}, expected=18+20},
}
local function setfenv(fn, env)
local i = 1
while true do
local name = debug.getupvalue(fn, i)
if name == "_ENV" then
debug.upvaluejoin(fn, i, (function() return env end), 1)
break
elseif not name then
break
end
i = i + 1
end
return fn
end
local techniques = {
["copy values over environment"]={
code="round(10*w/h) + a*b",
setup=function(code, fallback)
local env = setmetatable({},{__index=fallback})
return {env=env,func=load("return "..code,nil,nil,env)}
end,
call=function(block, kvs)
for k,v in pairs(block.env) do block.env[k]=nil end
for k,v in pairs(kvs) do block.env[k]=v end
return block.func()
end
},
["blank env, change meta of scope"]={
code="round(10*w/h) + a*b",
setup=function(code, fallback)
local kvsmeta = {__index=fallback}
local envmeta = {}
local env = setmetatable({},envmeta)
return {envmeta=envmeta,meta=meta,kvsmeta=kvsmeta,func=load("return "..code,nil,nil,env)}
end,
call=function(block, kvs)
block.envmeta.__index=kvs
setmetatable(kvs, block.kvsmeta)
return block.func()
end
},
["setfenv, change scope meta"]={
code="round(10*w/h) + a*b",
setup=function(code, fallback)
return {meta={__index=fallback}, func=load("return "..code)}
end,
call=function(block, kvs)
setmetatable(kvs,block.meta)
setfenv(block.func, kvs)
return block.func()
end
},
["Use __ENV, change scope meta"]={
code="round(10*w/h) + a*b",
setup=function(code, fallback)
local meta = {__index=fallback}
return {meta=meta, func=load("_ENV=... return "..code)}
end,
call=function(block, kvs)
return block.func(setmetatable(kvs, block.meta))
end
},
["scope as a table"]={
code="round(10*w/h) + _el.a * _el.b",
setup=function(code, fallback)
local env = setmetatable({},{__index=fallback})
return {env=env,func=load("return "..code,nil,nil,env)}
end,
call=function(block, kvs)
block.env._el=kvs
return block.func()
end
},
["scope as a table, 2"]={
code="round(10*w/h) + _el.a * _el.b",
setup=function(code, fallback)
return load("local _el=... return "..code,nil,nil,fallback)
end,
call=function(func, kvs)
return func(kvs)
end
},
}
function validate()
for name,technique in pairs(techniques) do
local f = technique.setup(technique.code, SANDBOX)
for i,test in ipairs(TESTS) do
local actual = technique.call(f, test.env)
if actual~=test.expected then
local err = ("%s test #%d expected %d but got %s\n"):format(name, i, test.expected, tostring(actual))
io.stderr:write(err)
error(-1)
end
end
end
end
local N = 1e6
function benchmark(setup, call)
for name,technique in pairs(techniques) do
local f = technique.setup(technique.code, SANDBOX)
local start = os.clock()
for i=1,N do
for i,test in ipairs(TESTS) do
technique.call(f, test.env)
end
end
local elapsed = os.clock() - start
print(("%-33s: %.1fs (%.2fµs per eval)"):format(name, elapsed, 1e6*elapsed/#TESTS/N))
end
end
validate()
benchmark()