WoW:USERAPI Memorizing table - Revision history

Move page script: Move page script moved page USERAPI Memorizing table to WoW:USERAPI Memorizing table without leaving a redirect

2023-08-15T04:49:13Z

Move page script moved page USERAPI Memorizing table to USERAPI Memorizing table without leaving a redirect

← Older revision	Revision as of 04:49, 15 August 2023
(No difference)

Bear at 07:54, 18 May 2020

2020-05-18T07:54:04Z

← Older revision		Revision as of 07:54, 18 May 2020
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	{{userfunc}}		{{userfunc}}
	~~__NOTOC__~~

	A '''memoizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks it's just doing a normal lookup.		A '''memoizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks it's just doing a normal lookup.

WoWWiki>Rolandius: Corrected spelling/grammar

2009-01-24T07:22:39Z

Corrected spelling/grammar

← Older revision		Revision as of 07:22, 24 January 2009
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	== Code ==		== Code ==
	For this example we will cache the name results from a [[API GetItemInfo\|GetItemInfo]] call.		For this example, we will cache the name results from a [[API GetItemInfo\|GetItemInfo]] call.

	local names = setmetatable({}, {		local names = setmetatable({}, {
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	return name		return name
	end,		end,
	})		})

	== How it works ==		== How it works ==

WoWWiki>WoWWiki-Wobin: Typo fixed to a more precise definition

2007-06-14T03:37:27Z

Typo fixed to a more precise definition

← Older revision		Revision as of 03:37, 14 June 2007
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	__NOTOC__		__NOTOC__

	A '''~~memorizing~~ table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks it's just doing a normal lookup.		A '''memoizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks it's just doing a normal lookup.

	~~Memorizing~~ tables are especially handy for caching values which are expensive to lookup or calculate. The developer generally expects that for a given index the value won't change, so it does not need to be recomputed after the first lookup.		Memoizing tables are especially handy for caching values which are expensive to lookup or calculate. The developer generally expects that for a given index the value won't change, so it does not need to be recomputed after the first lookup.

	== Code ==		== Code ==

WoWWiki>Tekkub: New page: {{userfunc}} NOTOC A '''memorizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks i...

2007-06-14T03:14:22Z

New page: {{userfunc}} __NOTOC__ A '''memorizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks i...

New page

{{userfunc}}
__NOTOC__

A '''memorizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks it's just doing a normal lookup.

Memorizing tables are especially handy for caching values which are expensive to lookup or calculate. The developer generally expects that for a given index the value won't change, so it does not need to be recomputed after the first lookup.

== Code ==
For this example we will cache the name results from a [[API GetItemInfo|GetItemInfo]] call.

local names = setmetatable({}, {
__index = function(t, i)
local name = GetItemInfo(i)
if not name then return end
rawset(t, i, name)
return name
end,
})

== How it works ==
At first glance, this code is rather arcane. We will dissect it line by line.

local names = setmetatable({}, {
This creates a new table <code>{}</code> to store values in. We set the metatable in the lines following this call. <code>setmetatable</code> returns back the table passed as the first arg, so we save it.

__index = function(t, i)
This is where the real magic begins. If we perform a lookup, for example <code>names[1234]</code> the names table is queried for index 1234. If there is a value here it is returned, a plain simple metatable-less lookup. But what if the value is nil? Lua sees our table has a metatable with a __index function, so it calls this function. The table and the requested index are passed, the same as if we had called <code>__index(names, 1234)</code>

local name = GetItemInfo(i)
if not name then return end
Simple enough, this is where we look up our value, and return out if nothing is found.

rawset(t, i, name)
return name
If we didn't return out, we found a name. We use rawset to save the value into our table (for future lookups) and we return the result back for the caller's use.

WoW:USERAPI Memorizing table - Revision history

Move page script: Move page script moved page USERAPI Memorizing table to WoW:USERAPI Memorizing table without leaving a redirect

Bear at 07:54, 18 May 2020

WoWWiki>Rolandius: Corrected spelling/grammar

WoWWiki>WoWWiki-Wobin: Typo fixed to a more precise definition

WoWWiki>Tekkub: New page: {{userfunc}} __NOTOC__ A '''memorizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks i...

WoWWiki>Tekkub: New page: {{userfunc}} NOTOC A '''memorizing table''' is a normal table with a metatable designed to find missing values and save them. The mechanics are transparent to the caller, it thinks i...