Re: Soliciting criticism of memoize function
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- Subject: Re: Soliciting criticism of memoize function
- From: "Eric Tetz" <erictetz@...>
- Date: 2008年5月16日 14:23:54 -0700
On Wed, May 14, 2008 at 6:40 PM, Norman Ramsey <nr@eecs.harvard.edu> wrote:
> I would be pleased if readers of this list could think of any improvements
> to the following memoize function:
Your code isn't testing for 'f' returning no values (which may or may
not be what you want).
I don't see why the 'update' closure is needed. Wouldn't it be more
straightforward to just say:
function memoize (f)
-- f must take at most one argument and return at most one result
local cache = setmetatable({ }, { __mode = 'k' })
return function (x, extra)
assert(extra == nil) -- cache works with at most one arg
local v = cache[x]
if not v then
v, extra = f(x)
assert(extra == nil) -- cache works with at most one return value
cache[x] = v
end
return v
end
end
Also, it's easy to allow f to return any number of values (unless
there's a reason you forbid that):
function memoize (f)
-- f must take at most one argument
local cache = setmetatable({ }, { __mode = 'k' })
return function (x, extra)
assert(extra == nil) -- cache works with at most one arg
local v = cache[x]
if not v then
v = { f(x) } -- save all return values
cache[x] = v
end
return unpack(v)
end
end
Cheers,
Eric