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WoW:HOWTO: Use Tables Without Generating Extra Garbage (source)
Revision as of 06:25, 23 May 2020
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Creating number and strings values is pretty efficient in Lua, Numbers do not have any additional data structure associated with them and are freed immediately when no longer used. Strings are hashed and stacked together with same strings, so creating 10000 copies of "Hello, world!" or creating and freeing it repeatedly will not produce garbage. Tables, however, always take memory when created that always becomes garbage when table is no longer used. If you do not want to create unnecessary garbage either avoid using tables unless it is really necessary or, in case several of your throw-away tables use same set of fields, or each new calculation uses superset of field of previous table, use only one table instead of creating new table for every calculation. For example, if you need to sort 20 values, display result and then sort another 30 and display them too, most people would write: | Creating number and strings values is pretty efficient in Lua, Numbers do not have any additional data structure associated with them and are freed immediately when no longer used. Strings are hashed and stacked together with same strings, so creating 10000 copies of "Hello, world!" or creating and freeing it repeatedly will not produce garbage. Tables, however, always take memory when created that always becomes garbage when table is no longer used. If you do not want to create unnecessary garbage either avoid using tables unless it is really necessary or, in case several of your throw-away tables use same set of fields, or each new calculation uses superset of field of previous table, use only one table instead of creating new table for every calculation. For example, if you need to sort 20 values, display result and then sort another 30 and display them too, most people would write: | ||
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Finally, let me stress once again: this works best when you have table of same size or with same set of fields. As you see from the last example, buttons differ by two fields and function now has to take care of that. Forgetting this while using this approach can produce some very funny and hard to track bugs. And clearing table from previous values can degrade performance if there are many fields to clear on each run. Another thing to be aware of is that unlike <tt>UIDropDownMenu_AddButton</tt>, some function may store table reference and check values from it at some point in future, hoping that nobody else uses this table. When such function do that in future only to get something else that was initially passed, they tend to mess things up in quite spectacular ways. Check the target function to make sure that it doesn't store passed table. | Finally, let me stress once again: this works best when you have table of same size or with same set of fields. As you see from the last example, buttons differ by two fields and function now has to take care of that. Forgetting this while using this approach can produce some very funny and hard to track bugs. And clearing table from previous values can degrade performance if there are many fields to clear on each run. Another thing to be aware of is that unlike <tt>UIDropDownMenu_AddButton</tt>, some function may store table reference and check values from it at some point in future, hoping that nobody else uses this table. When such function do that in future only to get something else that was initially passed, they tend to mess things up in quite spectacular ways. Check the target function to make sure that it doesn't store passed table. | ||
[[Category:HOWTOs|Use Tables Without Generating Extra Garbage]] | [[Category:HOWTOs|Use Tables Without Generating Extra Garbage]] | ||