¿Qué son los datos de usuario en Lua?

What is userdata in Lua?

The type userdata is provided to allow arbitrary C data to be stored in Lua variables. A userdata value is a pointer to a block of raw memory. There are two kinds of userdata: full userdata, where the block of memory is managed by Lua, and light userdata, where the block of memory is managed by the host.

Moreover, Lua does not even offer pointers to other objects, such as tables or functions. So, we cannot refer to Lua objects through pointers. Instead, when we need such pointers, we create a reference and store it in C.

In Lua, userdata is data that cannot be described in any of the other basic Lua types. HideData types. Basic Lua types. nil · boolean · number · string · function · userdata · table. Roblox types.

Any data the user creates or owns. The term user data may be used to emphasize that the data were created and owned by the user. In this case, the user data would typically be custom settings made in the app and stored in a separate file.

The void type in C++ is the type of the result of a function that returns normally but does not provide a result value to its caller. When these functions are called from Lua, the result value is nil.

Although arguments to Lua functions are passed by value, meaning they’re duplicates, and although local variables in functions are passed by value as returns, arguments and returns of tables are a special case, because tables are ALWAYS passed and assigned by REFERENCE! Tables are passed and assigned by reference.

Metatables allow us to store metadata about data and alter the behaviour of data. Roblox only allows us to give tables a metatable. Normally, tables only have a few operations. We can associate a key with a value, get the value associated with a key, and check for strict equality between two tables.

By default, user data scripts and cloud-init directives run only during the first boot cycle when an EC2 instance is launched. However, you can configure your user data script and cloud-init directives with a mime multi-part file.

The cloud-init package configures specific aspects of a new Amazon Linux instance when it is launched; most notably, it configures the . ssh/authorized_keys file for the ec2-user so you can log in with your own private key. For more information, see cloud-init.

A light userdatum is a value that represents a C pointer (that is, a void * value). Because it is a value, we do not create them (in the same way that we do not create numbers). To put a light userdatum into the stack, we use lua_pushlightuserdata : Despite their common name, light userdata are quite different from full userdata.

A heavy userdatum represents a region of mutable bytes allocated in Lua’s memory and managed by Lua (garbage collected). This is the only memory in Lua that you are permitted to read/write directly from C (via the userdata’s pointer) without the C API. Light userdata have the semantics of values, while heavy userdata have the semantics of objects.

Like numbers are equal when they have the same value, light userdata compare equal when they hold the same pointer. Like numbers, they exist as long as they are on the stack or stored in a variable, and they do not have individual metatables and they are not garbage collected.

A key distinction from malloc () is that you never need to call free (), rather you just allow the last reference to it to evaporate and the garbage collector will reclaim its storage eventually. They are most useful for holding data that is useful from C, but which must be managed from Lua.