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DF structures described by the xml files in library/xml are exported to lua code as a tree of objects and functions under the df global, which broadly maps to the df namespace in C++.
WARNING: The wrapper provides almost raw access to the memory of the game, so mistakes in manipulating objects are as likely to crash the game as equivalent plain C++ code would be. E.g. NULL pointer access is safely detected, but dangling pointers aren't.
Objects managed by the wrapper can be broadly classified into the following groups:
Typed object pointers (references).
References represent objects in DF memory with a known type.
In addition to fields and methods defined by the wrapped type, every reference has some built-in properties and methods.
Untyped pointers
Represented as lightuserdata.
In assignment to a pointer NULL can be represented either as nil, or a NULL lightuserdata; reading a NULL pointer field returns nil.
Named types
Objects in the df tree that represent identity of struct, class, enum and bitfield types. They host nested named types, static methods, builtin properties & methods, and, for enums and bitfields, the bi-directional mapping between key names and values.
The global object
df.global corresponds to the df::global namespace, and behaves as a mix between a named type and a reference, containing both nested types and fields corresponding to global symbols.
In addition to the global object and top-level types the df global also contains a few global builtin utility functions.
The underlying primitive lua object is userdata with a metatable. Every structured field access produces a new userdata instance.
All typed objects have the following built-in features:
ref1 == ref2, tostring(ref)
References implement equality by type & pointer value, and string conversion.
pairs(ref)
Returns an iterator for the sequence of actual C++ field names and values. Fields are enumerated in memory order. Methods and lua wrapper properties are not included in the iteration.
ref._kind
Returns one of: primitive, struct, container, or bitfield, as appropriate for the referenced object.
ref._type
Returns the named type object or a string that represents the referenced object type.
ref:sizeof()
Returns size, address
ref:new()
Allocates a new instance of the same type, and copies data from the current object.
ref:delete()
Destroys the object with the C++ delete operator. If destructor is not available, returns false.
WARNING: the lua reference object remains as a dangling pointer, like a raw C++ pointer would.
ref:assign(object)
Assigns data from object to ref. Object must either be another ref of a compatible type, or a lua table; in the latter case special recursive assignment rules are applied.
ref:_displace(index[,step])
Returns a new reference with the pointer adjusted by index*step. Step defaults to the natural object size.
References of the _kind 'primitive' are used for objects that don't fit any of the other reference types. Such references can only appear as a value of a pointer field, or as a result of calling the _field() method.
They behave as structs with one field value of the right type.
Struct references are used for class and struct objects.
They implement the following features:
ref.field, ref.field = value
Valid fields of the structure may be accessed by subscript.
Primitive typed fields, i.e. numbers & strings, are converted to/from matching lua values. The value of a pointer is a reference to the target, or nil/NULL. Complex types are represented by a reference to the field within the structure; unless recursive lua table assignment is used, such fields can only be read.
NOTE: In case of inheritance, superclass fields have precedence over the subclass, but fields shadowed in this way can still be accessed as ref['subclasstype.field']. This shadowing order is necessary because vtable-based classes are automatically exposed in their exact type, and the reverse rule would make access to superclass fields unreliable.
ref._field(field)
Returns a reference to a valid field. That is, unlike regular subscript, it returns a reference to the field within the structure even for primitive typed fields and pointers.
ref:vmethod(args...)
Named virtual methods are also exposed, subject to the same shadowing rules.
pairs(ref)
Enumerates all real fields (but not methods) in memory (= declaration) order.
Containers represent vectors and arrays, possibly resizable.
A container field can associate an enum to the container reference, which allows accessing elements using string keys instead of numerical indices.
Implemented features:
ref._enum
If the container has an associated enum, returns the matching named type object.
#ref
Returns the length of the container.
ref[index]
Accesses the container element, using either a 0-based numerical index, or, if an enum is associated, a valid enum key string.
Accessing an invalid index is an error, but some container types may return a default value, or auto-resize instead for convenience. Currently this relaxed mode is implemented by df-flagarray aka BitArray.
ref._field(index)
Like with structs, returns a pointer to the array element, if possible. Flag and bit arrays cannot return such pointer, so it fails with an error.
pairs(ref), ipairs(ref)
If the container has no associated enum, both behave identically, iterating over numerical indices in order. Otherwise, ipairs still uses numbers, while pairs tries to substitute enum keys whenever possible.
ref:resize(new_size)
Resizes the container if supported, or fails with an error.
ref:insert(index,item)
Inserts a new item at the specified index. To add at the end, use #ref as index.
ref:erase(index)
Removes the element at the given valid index.
Bitfields behave like special fixed-size containers. The _enum property points to the bitfield type.
Numerical indices correspond to the shift value, and if a subfield occupies multiple bits, the ipairs order would have a gap.
Named types are exposed in the df tree with names identical to the C++ version, except for the :: vs . difference.
All types and the global object have the following features:
type._kind
Evaluates to one of struct-type, class-type, enum-type, bitfield-type or global.
type._identity
Contains a lightuserdata pointing to the underlying DFHack::type_instance object.
Types excluding the global object also support:
type:sizeof()
Returns the size of an object of the type.
type:new()
Creates a new instance of an object of the type.
type:is_instance(object)
Returns true if object is same or subclass type, or a reference to an object of same or subclass type. It is permissible to pass nil, NULL or non-wrapper value as object; in this case the method returns nil.
In addition to this, enum and bitfield types contain a bi-directional mapping between key strings and values, and also map _first_item and _last_item to the min and max values.
Struct and class types with instance-vector attribute in the xml have a type.find(key) function that wraps the find method provided in C++.
The df table itself contains the following functions and values:
NULL, df.NULL
Contains the NULL lightuserdata.
df.isnull(obj)
Evaluates to true if obj is nil or NULL; false otherwise.
df.isvalid(obj[,allow_null])
For supported objects returns one of type, voidptr, ref.
If allow_null is true, and obj is nil or NULL, returns null.
Otherwise returns nil.
df.sizeof(obj)
For types and refs identical to obj:sizeof(). For lightuserdata returns nil, address
df.new(obj), df.delete(obj), df.assign(obj, obj2)
Equivalent to using the matching methods of obj.
df._displace(obj,index[,step])
For refs equivalent to the method, but also works with lightuserdata (step is mandatory then).
df.is_instance(type,obj)
Equivalent to the method, but also allows a reference as proxy for its type.
Recursive assignment is invoked when a lua table is assigned to a C++ object or field, i.e. one of:
The general mode of operation is that all fields of the table are assigned to the fields of the target structure, roughly emulating the following code:
function rec_assign(ref,table)
for key,value in pairs(table) do
ref[key] = value
end
end
Since assigning a table to a field using = invokes the same process, it is recursive.
There are however some variations to this process depending on the type of the field being assigned to:
If the table contains an assign field, it is applied first, using the ref:assign(value) method. It is never assigned as a usual field.
When a table is assigned to a non-NULL pointer field using the ref.field = {...} syntax, it is applied to the target of the pointer instead.
If the pointer is NULL, the table is checked for a new field:
After this auto-vivification process, assignment proceeds as if the pointer wasn't NULL.
Obviously, the new field inside the table is always skipped during the actual per-field assignment processing.
If the target of the assignment is a container, a separate rule set is used:
If the table contains neither assign nor resize fields, it is interpreted as an ordinary 1-based lua array. The container is resized to the #-size of the table, and elements are assigned in numeric order:
ref:resize(#table); for i=1,#table do ref[i-1] = table[i] end
Otherwise, resize must be true, false, or an explicit number. If it is not false, the container is resized. After that the usual struct-like 'pairs' assignment is performed.
In case resize is true, the size is computed by scanning the table for the largest numeric key.
This means that in order to reassign only one element of a container using this system, it is necessary to use:
{ resize=false, [idx]=value }
Since nil inside a table is indistinguishable from missing key, it is necessary to use df.NULL as a null pointer value.
This system is intended as a way to define a nested object tree using pure lua data structures, and then materialize it in C++ memory in one go. Note that if pointer auto-vivification is used, an error in the middle of the recursive walk would not destroy any objects allocated in this way, so the user should be prepared to catch the error and do the necessary cleanup.
DFHack utility functions are placed in the dfhack global tree.
Currently it defines the following features:
dfhack.print(args...)
Output tab-separated args as standard lua print would do, but without a newline.
print(args...), dfhack.println(args...)
A replacement of the standard library print function that works with DFHack output infrastructure.
dfhack.printerr(args...)
Same as println; intended for errors. Uses red color and logs to stderr.log.
dfhack.color([color])
Sets the current output color. If color is nil or -1, resets to default.
dfhack.is_interactive()
Checks if the thread can access the interactive console and returns true or false.
dfhack.lineedit([prompt[,history_filename]])
If the thread owns the interactive console, shows a prompt and returns the entered string. Otherwise returns nil, error.
dfhack.interpreter([prompt[,env[,history_filename]]])
Starts an interactive lua interpreter, using the specified prompt string, global environment and command-line history file.
If the interactive console is not accessible, returns nil, error.
dfhack.pcall(f[,args...])
Invokes f via xpcall, using an error function that attaches a stack trace to the error. The same function is used by SafeCall in C++, and dfhack.safecall.
The returned error is a table with separate message and stacktrace string fields; it implements __tostring.
safecall(f[,args...]), dfhack.safecall(f[,args...])
Just like pcall, but also prints the error using printerr before returning. Intended as a convenience function.
dfhack.with_suspend(f[,args...])
Calls f with arguments after grabbing the DF core suspend lock. Suspending is necessary for accessing a consistent state of DF memory.
Returned values and errors are propagated through after releasing the lock. It is safe to nest suspends.
Every thread is allowed only one suspend per DF frame, so it is best to group operations together in one big critical section. A plugin can choose to run all lua code inside a C++-side suspend lock.
This api is intended for storing configuration options in the world itself. It probably should be restricted to data that is world-dependent.
Entries are identified by a string key, but it is also possible to manage multiple entries with the same key; their identity is determined by entry_id. Every entry has a mutable string value, and an array of 7 mutable ints.
dfhack.persistent.get(key), entry:get()
Retrieves a persistent config record with the given string key, or refreshes an already retrieved entry. If there are multiple entries with the same key, it is undefined which one is retrieved by the first version of the call.
Returns entry, or nil if not found.
dfhack.persistent.delete(key), entry:delete()
Removes an existing entry. Returns true if succeeded.
dfhack.persistent.get_all(key[,match_prefix])
Retrieves all entries with the same key, or starting with key..'/'. Calling get_all('',true) will match all entries.
If none found, returns nil; otherwise returns an array of entries.
dfhack.persistent.save({key=str1, ...}[,new]), entry:save([new])
Saves changes in an entry, or creates a new one. Passing true as new forces creation of a new entry even if one already exists; otherwise the existing one is simply updated. Returns entry, did_create_new
Since the data is hidden in data structures owned by the DF world, and automatically stored in the save game, these save and retrieval functions can just copy values in memory without doing any actual I/O. However, currently every entry has a 180+-byte dead-weight overhead.