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Learning it recently for a small game design, I was surprised that you couldnt easily copy a table, and even more suprised you needed "metatables" to do it...th

by petee 4y ago

Learning it recently for a small game design, I was surprised that you couldnt easily copy a table, and even more suprised you needed "metatables" to do it...the extra steps seem far from simple. Maybe I'm just missing something. If I recall, I was simply trying to create a new 'object' (game character) from a template but it required metatable boiler plate that just made no sense to me. Many languages, this is simply a = b, or at most allocating some space first.

boffinAudio 4y ago
You might find it handy to add lua-enumerable.lua to your standard set of Lua-project modules: https://github.com/mikelovesrobots/lua-enumerable/blob/master/lua-enumerable.lua https://github.com/mikelovesrobots/lua-enumerable/blob/maste... See: table.dup()
- nmz 4y ago
  NOTE: Doesn't copy metamethods, doesn't copy subtables either.
DayDollar 4y ago
In many scripting languages this is not the case, and you are ever only passing around references. Python comes to mind. Lots of people obviously have a problem with this as it deeply different from the algebra derived assignment syntax. local a = b creates a local copy, but even then, its not a deepcopy, containing references to other tables.
- kzrdude 4y ago
  python has both .copy() methods and a copy module. That's not to highlight Python's strengths, but an indication that it's a complex topic in Python - it has footguns here. The copy module might even do the wrong thing for a given object.
- naniwaduni 4y ago
  The algebra-derived assignment syntax kind of falls apart with mutation anyway.
scythe 4y ago
>I was surprised that you couldn't easily copy a table Lua's designers have a sort of maxim "if it can't be done perfectly, let the user roll their own". This can be frustrating, but for table-copying it's not surprising. Do you copy subtables by reference or value? What about recursive tables? Mutually recursive subtables? Closures in tables? And then userdata can contain references that are opaque to the language runtime. It's not easy to define the behavior of deep copy in the fully general case.

by petee 4y ago

boffinAudio 4y ago

You might find it handy to add lua-enumerable.lua to your standard set of Lua-project modules: https://github.com/mikelovesrobots/lua-enumerable/blob/master/lua-enumerable.lua https://github.com/mikelovesrobots/lua-enumerable/blob/maste... See: table.dup()

nmz 4y ago
NOTE: Doesn't copy metamethods, doesn't copy subtables either.

DayDollar 4y ago

In many scripting languages this is not the case, and you are ever only passing around references. Python comes to mind. Lots of people obviously have a problem with this as it deeply different from the algebra derived assignment syntax. local a = b creates a local copy, but even then, its not a deepcopy, containing references to other tables.

kzrdude 4y ago
python has both .copy() methods and a copy module. That's not to highlight Python's strengths, but an indication that it's a complex topic in Python - it has footguns here. The copy module might even do the wrong thing for a given object.
naniwaduni 4y ago
The algebra-derived assignment syntax kind of falls apart with mutation anyway.

scythe 4y ago

>I was surprised that you couldn't easily copy a table Lua's designers have a sort of maxim "if it can't be done perfectly, let the user roll their own". This can be frustrating, but for table-copying it's not surprising. Do you copy subtables by reference or value? What about recursive tables? Mutually recursive subtables? Closures in tables? And then userdata can contain references that are opaque to the language runtime. It's not easy to define the behavior of deep copy in the fully general case.