I have a C++ class which acts like a map that can contain different data types.
In C++, it is unknown at compile time what data type an entry is. Therefore, the programmer has to know and the accessor is templated:
auto a = map.get<int>("my-int-entry");
auto b = map.get<std::string>("my-string-entry");
At runtime, the map knows what type the entries have. So in python, I should be able to use the runtime type information.
a = map.get('my-int-entry') # a is of type int
b = map.get('my-string-entry') # b is of type string
I'd like that it looks up the type information at runtime, then calls get<int> if the runtime type is int, otherwise get<std::string>. Is there a way to do this directly in pybind11?
Or do I need another (pure python) function that calls the respectively mapped C++ functions?
I'm not sure how you would query your map in runtime about what type a key has, but this is the general idea of how I would do that:
map_wrapper.def("get", [](Map& self, const std::string& key) -> py::object {
if (self.is_a<int>(key)) {
return py::cast(self.get<int>(key));
} else if (self.is_a<std::string>(key)) {
return py::cast(self.get<std::string>(key));
} else if ...
});
You would need to know the types you want to support in advance.
Related
I'm going to request some user configuration via json from the server that contains two types of data like (usrID, bool), and (usrID, int). so, I created two map to classify and reload two functions with the same name to put the data into the corresponding map after parsed.
For the sake of refinement, I used the auto keyword of C++11 to initialize a variable without assign and determined its type whether bool or int mentioned above through assigned by parse function, so as to call the overloaded function directly to store them.
But it causes compiler error that cannot use a auto variable without assign.
bool fromStringtoBool() {……}
int fromStringtoInt() {……}
void setAppidConfig(int,bool);
void setAppidConfig(int,int);
……
……
void main func()
{
……
int usrId;
auto value;
if(isBool())
{
value = fromStringtoBool();
}
else
{
value = fromStringtoInt();
}
setAppidConfig(usrId,value)
……
}
Is it possible to implement the above logic in C++ ?
No. In C++ auto variable type resolution and also function overload resolution has to happen compile time. The isBool() of yours is presumably runtime value. So all you can do is something like:
if(isBool())
{
setAppidConfig(usrId,fromStringtoBool());
}
else
{
setAppidConfig(usrId,fromStringtoInt());
}
auto allows you to omit the type name and let the compiler deduce the type. There is no type to deduce from in your case, since there's no assignment, so nothing can be deduced.
For your use case, you need some kind of variant type that can store one of several types. The Qt library has QVariant, and other libraries usually offer something like that as well. As of C++17 however, such a type is offered directly by the standard library: std::variant.
int usrId;
std::variant<bool, int> value;
if (isBool()) {
value = fromStringtoBool();
} else {
value = fromStringtoInt();
}
setAppidConfig(usrId, value);
The setAppidConfig() function would need to accept an appropriate variant parameter:
void setAppidConfig(int usrId, std::variant<bool, int> value)
{
// ...
if (std::holds_alternative<int>(value)) {
// It's a int.
int i = std::get<int>(value);
} else {
// It's a bool.
bool b = std::get<bool>(value);
}
}
Note that variants can hold more than just two types (you can have an std::variant<bool, int, std::string> for example.)
If you need something that can hold anything, then you can use an std::any. This type does not need to know the types in advance (it takes no template arguments.)
I extended the LLVM Kaleidoscope example to support Strings. I added a StringExprAST, which has the virtual Codegen method impl as follows:
Value *StringExprAST::Codegen() {
StringRef r(Val);
return ConstantDataArray::getString(getGlobalContext(), r, false);
}
I am trying to concatenate Strings and have a ConcatExprAST with its Codegen method. Upon trying to access the data in the ConstantDataArray, I need to cast the Value* back to a ConstantDataArray* in order to use the getAsString() method.
How can I do this?
Thanks for any help.
The proper way to cast any subtype of Value to another is via cast<>(), e.g.:
Value* v = ...
ConstantDataArray* result = cast<ConstantDataArray>(v);
However, keep in mind that in your example you don't return an object of type ConstantDataArray, but you return something of the return type of ConstantDataArray::getString(), which is not necessarily an instance of ConstantDataArray itself, all you know is that it's a Constant (for instance, it might be a ConstantAggregateZero, which is not a ConstantDataArray).
In any case, if you're not sure that v is indeed of a specific type, check it first with isa<>() (or use the dyn_cast<>() idiom), before performing the cast<>().
I'm using luabind 0.9.1 from Ryan Pavlik's master distribution with Lua 5.1, cygwin on Win XP SP3 + latest patches x86, boost 1.48, gcc 4.3.4. Lua and boost are cygwin pre-compiled versions.
I've successfully built luabind in both static and shared versions.
Both versions pass all the tests EXCEPT for the test_object_identity.cpp test which fails in both versions.
I've tracked down the problem to the following issue:
If an entry in a table is created for NON built-in class (i.e., not int, string, etc), the value CANNOT be retrieved.
Here's a code piece that demonstrates this:
#include "test.hpp"
#include <luabind/luabind.hpp>
#include <luabind/detail/debug.hpp>
using namespace luabind;
struct test_param
{
int obj;
};
void test_main(lua_State* L)
{
using namespace luabind;
module(L)
[
class_<test_param>("test_param")
.def_readwrite("obj", &test_param::obj)
];
test_param temp_object;
object tabc = newtable(L);
tabc[1] = 10;
tabc[temp_object] = 30;
TEST_CHECK( tabc[1] == 10 ); // passes
TEST_CHECK( tabc[temp_object] == 30 ); // FAILS!!!
}
tabc[1] is indeed 10 while tabc[temp_object] is NOT 30! (actually, it seems to be nil)
However, if I use iterate to go over tabc entries, there're the two entries with the CORRECT key/value pairs.
Any ideas?
BTW, overloading the == operator like this:
#include <luabind/operator.hpp>
struct test_param
{
int obj;
bool operator==(test_param const& rhs) const
{
return obj == rhs.obj;
}
};
and
module(L)
[
class_<test_param>("test_param")
.def_readwrite("obj", &test_param::obj)
.def(const_self == const_self)
];
Doesn't change the result.
I also tried switching to settable() and gettable() from the [] operator. The result is the same. I can see with the debugger that default conversion of the key is invoked, so I guess the error arises from somewhere therein, but it's beyond me to figure out what exactly the problem is.
As the following simple test case show, there're definitely a bug in Luabind's conversion for complex types:
struct test_param : wrap_base
{
int obj;
bool operator==(test_param const& rhs) const
{ return obj == rhs.obj ; }
};
void test_main(lua_State* L)
{
using namespace luabind;
module(L)
[
class_<test_param>("test_param")
.def(constructor<>())
.def_readwrite("obj", &test_param::obj)
.def(const_self == const_self)
];
object tabc, zzk, zzv;
test_param tp, tp1;
tp.obj = 123456;
// create new table
tabc = newtable(L);
// set tabc[tp] = 5;
// o k v
settable( tabc, tp, 5);
// get access to entry through iterator() API
iterator zzi(tabc);
// get the key object
zzk = zzi.key();
// read back the value through gettable() API
// o k
zzv = gettable(tabc, zzk);
// check the entry has the same value
// irrespective of access method
TEST_CHECK ( *zzi == 5 &&
object_cast<int>(zzv) == 5 );
// convert key to its REAL type (test_param)
tp1 = object_cast<test_param>(zzk);
// check two keys are the same
TEST_CHECK( tp == tp1 );
// read the value back from table using REAL key type
zzv = gettable(tabc, tp1);
// check the value
TEST_CHECK( object_cast<int>(zzv) == 5 );
// the previous call FAILS with
// Terminated with exception: "unable to make cast"
// this is because gettable() doesn't return
// a TRUE value, but nil instead
}
Hopefully, someone smarter than me can figure this out,
Thx
I've traced the problem to the fact that Luabind creates a NEW DISTINCT object EVERY time you use a complex value as key (but it does NOT if you use a primitive one or an object).
Here's a small test case that demonstrates this:
struct test_param : wrap_base
{
int obj;
bool operator==(test_param const& rhs) const
{ return obj == rhs.obj ; }
};
void test_main(lua_State* L)
{
using namespace luabind;
module(L)
[
class_<test_param>("test_param")
.def(constructor<>())
.def_readwrite("obj", &test_param::obj)
.def(const_self == const_self)
];
object tabc, zzk, zzv;
test_param tp;
tp.obj = 123456;
tabc = newtable(L);
// o k v
settable( tabc, tp, 5);
iterator zzi(tabc), end;
std::cerr << "value = " << *zzi << "\n";
zzk = zzi.key();
// o k v
settable( tabc, tp, 6);
settable( tabc, zzk, 7);
for (zzi = iterator(tabc); zzi != end; ++zzi)
{
std::cerr << "value = " << *zzi << "\n";
}
}
Notice how tabc[tp] first has the value 5 and then is overwritten with 7 when accessed through the key object. However, when accessed AGAIN through tp, a new entry gets created. This is why gettable() fails subsequently.
Thx,
David
Disclaimer: I'm not an expert on luabind. It's entirely possible I've missed something about luabind's capabilities.
First of all, what is luabind doing when converting test_param to a Lua key? The default policy is copy. To quote the luabind documentation:
This will make a copy of the parameter. This is the default behavior when passing parameters by-value. Note that this can only be used when passing from C++ to Lua. This policy requires that the parameter type has an accessible copy constructor.
In pratice, what this means is that luabind will create a new object (called "full userdata") which is owned by the Lua garbage collector and will copy your struct into it. This is a very safe thing to do because it no longer matters what you do with the c++ object; the Lua object will stick around without really any overhead. This is a good way to do bindings for by-value sorts of objects.
Why does luabind create a new object each time you pass it to Lua? Well, what else could it do? It doesn't matter if the address of the passed object is the same, because the original c++ object could have changed or been destroyed since it was first passed to Lua. (Remember, it was copied to Lua by value, not by reference.) So, with only ==, luabind would have to maintain a list of every object of that type which had ever been passed to Lua (possibly weakly) and compare your object against each one to see if it matches. luabind doesn't do this (nor do I think should it).
Now, let's look at the Lua side. Even though luabind creates two different objects, they're still equal, right? Well, the first problem is that, besides certain built-in types, Lua can only hold objects by reference. Each of those "full userdata" that I mentioned before is actually a pointer. That means that they are not identical.
But they are equal, if we define an __eq meta operation. Unfortunately, Lua itself simply does not support this case. Userdata when used as table keys are always compared by identity, no matter what. This actually isn't special for userdata; it is also true for tables. (Note that to properly support this case, Lua would need to override the hashcode operation on the object in addition to __eq. Lua also does not support overriding the hashcode operation.) I can't speak for the authors of Lua why they did not allow this (and it has been suggested before), but there it is.
So, what are the options?
The simplest thing would be to convert test_param to an object once (explicitly), and then use that object to index the table both times. However, I suspect that while this fixes your toy example, it isn't very helpful in practice.
Another option is simply not to use such types as keys. Actually, I think this is a very good suggestion, since this kind of light-weight binding is quite useful, and the only other option is to discard it.
It looks like you can define a custom conversion on your type. In your example, it might be reasonable to convert your type to a Lua number which will behave well as a table index.
Use a different kind of binding. There will be some overhead, but if you want identity, you'll have to live with it. It sounds like luabind has some support for wrappers, which you may need to use to preserve identity:
When a pointer or reference to a registered class with a wrapper is passed to Lua, luabind will query for it's dynamic type. If the dynamic type inherits from wrap_base, object identity is preserved.
I need some advice how can I bind a C/C++ structure to Ruby. I've read some manuals and I found out how to bind class methods to a class, but I still don't understand how to bind structure fields and make them accessible in Ruby.
Here is the code I'm using:
myclass = rb_define_class("Myclass", 0);
...
typedef struct nya
{
char const* name;
int age;
} Nya;
Nya* p;
VALUE vnya;
p = (Nya*)(ALLOC(Nya));
p->name = "Masha";
p->age = 24;
vnya = Data_Wrap_Struct(myclass, 0, free, p);
rb_eval_string("def foo( a ) p a end"); // This function should print structure object
rb_funcall(0, rb_intern("foo"), 1, vnya); // Here I call the function and pass the object into it
The Ruby function seems to assume that a is a pointer. It prints the numeric value of the pointer instead of it's real content (i.e., ["Masha", 24]). Obviously the Ruby function can't recognize this object —I didn't set the object's property names and types.
How can I do this? Unfortunately I can't figure it out.
You have already wrapped your pointer in a Ruby object. Now all you have to do is define how it can be accessed from the Ruby world:
/* Feel free to convert this function to a macro */
static Nya * get_nya_from(VALUE value) {
Nya * pointer = 0;
Data_Get_Struct(value, Nya, pointer);
return pointer;
}
VALUE nya_get_name(VALUE self) {
return rb_str_new_cstr(get_nya_from(self)->name);
}
VALUE nya_set_name(VALUE self, VALUE name) {
/* StringValueCStr returns a null-terminated string. I'm not sure if
it will be freed when the name gets swept by the GC, so maybe you
should create a copy of the string and store that instead. */
get_nya_from(self)->name = StringValueCStr(name);
return name;
}
VALUE nya_get_age(VALUE self) {
return INT2FIX(get_nya_from(self)->age);
}
VALUE nya_set_age(VALUE self, VALUE age) {
get_nya_from(self)->age = FIX2INT(age);
return age;
}
void init_Myclass() {
/* Associate these functions with Ruby methods. */
rb_define_method(myclass, "name", nya_get_name, 0);
rb_define_method(myclass, "name=", nya_set_name, 1);
rb_define_method(myclass, "age", nya_get_age, 0);
rb_define_method(myclass, "age=", nya_set_age, 1);
}
Now that you can access the data your structure holds, you can simply define the high level methods in Ruby:
class Myclass
def to_a
[name, age]
end
alias to_ary to_a
def to_s
to_a.join ', '
end
def inspect
to_a.inspect
end
end
For reference: README.EXT
This is not a direct answer to your question about structures, but it is a general solution to the problem of porting C++ classes to Ruby.
You could use SWIG to wrap C/C++ classes, structs and functions. In the case of a structure, it's burning a house to fry an egg. However, if you need a tool to rapidly convert C++ classes to Ruby (and 20 other languages), SWIG might be useful to you.
In your case involving a structure, you just need to create a .i file which includes (in the simplest case) the line #include <your C++ library.h>.
P.S. Once more, it's not a direct answer to your question involving this one struct, but maybe you could make use of a more general solution, in which case this may help you.
Another option is to use RubyInline - it has limited support for converting C and Ruby types (such as int, char * and float) and it also has support for accessing C structurs - see accessor method in the API.
I need to make COM IntetrOp at runtime using reflections. My native COM Object's exposed methods have some parameters as pointers (DWORD*) and some double pointers (DWORD**) and some are user defined types(e.g SomeUDTType objSmeUDTType) and vice versa its pointer(i.e. SomeUDTType *pSomeUDTType).
Now for dynamic method invocation, we have single option for passing parameters as array of object i.e object[] and filling this array statically.
But I need to pass pointers and references and pointers to pointers. For now how can I be able to populate object array as mixed data of simple data types, pointers or references and pointers to pointers.
Working Example:
Native COM exposed method :
STDMETHODIMP MyCallableMethod(DWORD *value_1,BSTR *bstrName,WESContext **a_wesContext)
Translated by tlbimp.exe (COMInterop)
UDTINIDLLib.IRuntimeCalling.MyCallableMethod(ref uint, ref string, System.IntPtr)
Now calling these methods at runtime using reflection at runtime,
See here :
Assembly asembly = Assembly.LoadFrom("E:\\UDTInIDL\\Debug\\UDTINIDLLib.dll");
Type[] types = asembly.GetTypes();
Type type = null;
//foreach (Type oType in types)
{
try
{
type = asembly.GetType("UDTINIDLLib.RuntimeCallingClass");
}
catch (TypeLoadException e)
{
Console.WriteLine(e.Message);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
object parameters = new object[3];
Type CustomType = asembly.GetType("UDTINIDLLib.WESContext");
object oCustomType = Activator.CreateInstance(CustomType);
FieldInfo fieldInfo = CustomType.GetField("MachineName", BindingFlags.Public | BindingFlags.Instance);
string MachineName = "ss01-cpu-102";
string MachineIp = "127.0.0.1";
string Certificate = "UK/78T";
fieldInfo.SetValue(oCustomType, MachineName);
fieldInfo.SetValue(oCustomType, MachineIp);
fieldInfo.SetValue(oCustomType, Certificate);
object obj = Activator.CreateInstance(type);
MethodInfo mInfo = type.GetMethod("MyCallableMethod");
int lengthOfParams = mInfo.GetParameters().Length;
ParameterInfo [] oParamInfos = mInfo.GetParameters();
object[] a_params = new object[lengthOfParams];
int ValueType = 0;
for(int iCount = 0; iCount<lengthOfParams; iCount++)
{
a_params[iCount] = ???; //Now here this array should be populated with corresponding pointers and other objects (i.e WESContext's obj)
}
mInfo.Invoke(obj, a_params);
Hope code will clarifies ...If any any confusion do let me know I'll edit my question accordingly.
I am stuck here , I'll be obliged if you help me out.(I am confused about "dynamic" keyword might hope it solves the problem)
Is there any need to generate C++/CLI wrappers? and if in which context?
Regards
Usman
Just put the values of your arguments directly into the array. For out/ref parameters, the corresponding elements of the array will be replaced by new values returned by the function.
For the double pointer, by far the easiest approach is to use /unsafe and unmanaged pointers, like so (assuming the parameter is used by the method to return a value):
WESContext* pWesContext; // the returned pointer will end up here
IntPtr ppWesContext = (IntPtr)&pWesContext;
// direct call
MyCallableMethod(..., ppWesContext);
// reflection
a_params[3] = ppWesContext;
mInfo.Invoke(obj, a_params);
After you'll get the pointer to struct in pWesContext, you can use -> to access the members in C#. I'm not sure what memory management rules for your API are, though; it may be that you will, eventually, need to free that struct, but how exactly to do that should be described by the documentation of the API you're trying to call.