3.11. Userdata and UserPointersΒΆ

Squirrel allows the host application put arbitrary data chunks into a Squirrel value, this is possible through the data type userdata.:

SQUserPointer sq_newuserdata(HSQUIRRELVM v,SQUnsignedInteger size);

When the function sq_newuserdata is called, Squirrel allocates a new userdata with the specified size, returns a pointer to his payload buffer and push the object in the stack; at this point the application can do whatever it want with this memory chunk, the VM will automatically take cake of the memory deallocation like for every other built-in type. A userdata can be passed to a function or stored in a table slot. By default Squirrel cannot manipulate directly userdata; however is possible to assign a delegate to it and define a behavior like it would be a table. Because the application would want to do something with the data stored in a userdata object when it get deleted, is possible to assign a callback that will be called by the VM just before deleting a certain userdata. This is done through the API call sq_setreleasehook.:

typedef SQInteger (*SQRELEASEHOOK)(SQUserPointer,SQInteger size);

void sq_setreleasehook(HSQUIRRELVM v,SQInteger idx,SQRELEASEHOOK hook);

Another kind of userdata is the userpointer; this type is not a memory chunk like the normal userdata, but just a ‘void*’ pointer. It cannot have a delegate and is passed by value, so pushing a userpointer doesn’t cause any memory allocation.:

void sq_pushuserpointer(HSQUIRRELVM v,SQUserPointer p);