mirror of
https://git.lyx.org/repos/lyx.git
synced 2024-11-06 00:10:59 +00:00
6d678c927c
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@808 a592a061-630c-0410-9148-cb99ea01b6c8
96 lines
3.1 KiB
Plaintext
96 lines
3.1 KiB
Plaintext
|
|
1.0 Marshallers
|
|
===============
|
|
|
|
Marshallers offer the opportunity to control the emittion process, and
|
|
collate return values. By default signals have a marshaller which does
|
|
nothing, and throws away all but the last return value.
|
|
|
|
A marshaller can be any class with:
|
|
struct SomeMarshal
|
|
{
|
|
// both typedefs must be defined.
|
|
typedef Type1 InType;
|
|
typedef Type2 OutType;
|
|
|
|
// Return final return code.
|
|
OutType value();
|
|
|
|
// Return value if marshaller does not get built
|
|
static OutType default_value();
|
|
|
|
// Captures return codes and returns TRUE to stop emittion.
|
|
bool marshal(const InType&);
|
|
|
|
SomeMarshal();
|
|
};
|
|
|
|
The function marshal() will be called with the return value of each slot
|
|
connected to the signal as they are called. The emittion process can be
|
|
stopped by marshal() returning true.
|
|
|
|
Once all the slots have been called, value() is called to determine what
|
|
to return to the emitter. If the signal gets called and there is
|
|
nothing attached the default_value() is used.
|
|
|
|
2.0 Possible uses
|
|
=================
|
|
A marshaller could stop emittion when the signal had been handled:
|
|
struct StopOnTrue
|
|
{
|
|
typedef bool InType;
|
|
typedef bool OutType;
|
|
OutType return_value_;
|
|
|
|
OutType value() { return return_value_; }
|
|
static OutType default_value() { return false; }
|
|
bool marshal(const InType& val) { return_value_ = val; return val; }
|
|
|
|
StopOnTrue() : return_value_(false) {}
|
|
};
|
|
|
|
marshal() here returns true as soon as one of the things connected to the
|
|
signal returns true. It also keeps track of whether anything stopped the
|
|
emittion in the return_value_ member. This way when something emits the
|
|
signal, it can tell whether the signal was dealt with (signal.emit()
|
|
returns true) or not (signal.emit() returns false).
|
|
|
|
Now, if OutType was a list or a vector, marshal() could push_back() all
|
|
the values, returning to the emitter all the return values rather than just
|
|
one.
|
|
|
|
3.0 Standard Marshallers
|
|
========================
|
|
|
|
The following marshallers are provided by default.
|
|
|
|
Marshal<void>
|
|
Marshal<T>
|
|
Marshal<R> (untested, may not be portable)
|
|
FixedMarshal<T,V>
|
|
FastMarshal<T>
|
|
|
|
where
|
|
- T can be a type, class, or pointer
|
|
- R can be a reference
|
|
- V is the initial value of the marshaller
|
|
which is returned if nothing is connected.
|
|
|
|
All of the standard defined marshallers, with the exception of
|
|
FastMarshal, check for a possiblity of a skipped return code via
|
|
RetCode::check_ignore(). You can cause a return code to be
|
|
ignored by the marshaller by setting RetCode::ignore() prior to returning
|
|
to a function. Please note that you must be sure that you are returning to
|
|
signal call to use ignore(). Calling at other times may result in other
|
|
functions incorrectly skipping.
|
|
|
|
The check_ignore function is thread safe which may induce
|
|
unnecessary delays in slot calling. To avoid this overhead
|
|
either define the signal to have a void return or
|
|
use a FastMarshal.
|
|
|
|
(This will all be replaced by an exeption mechanism at some point;
|
|
however, current compiler technology is too slow for this to
|
|
work.)
|
|
|