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lualua-table

Clearing table alternatives in Lua

I want to clear a table but not sure which way is the best and does what different than each other. What are the differences among these:

tbl = {}

for k, v in pairs(tbl) do v = nil end

for k, v in pairs(tbl) do tbl[k] = nil end

Thanks.

Solution 
  • tbl = {}

    This doesn't so much clear the table as just create a new one. The old one might get garbage-collected, depengin on whether there are other references to it.

    for k, v in pairs(tbl) do v = nil end

    This does absolutely nothing. It's a waste of processing power.

    for k, v in pairs(tbl) do tbl[k] = nil end

    This actually empties the table without creating a new one. For small tables, this is often more performant than creating a new table, as it means less work for the GC, but that's a somewhat advanced optimization technique and it's not like clearing tables is always better.

    Note that pairs uses the next function, which can handle keys being removed while iterating.