Consider the following code which prints out the even numbers up to 20:
import std.stdio;
class count_to_ten{
static int opApply()(int delegate(ref int) dg) {
int i = 1;
int ret;
while(i <= 10){
ret = dg(i);
if(ret != 0) {
break;
}
i++;
}
return ret;
}
}
void main() {
int y = 2;
foreach(int x; count_to_ten) {
writeln(x * y);
}
}
The syntax of opApply requires that it take a delegate or function as a normal argument. However, even if we relaxed that and allowed opApply to take a function as a template argument, we still would have no recourse for delegates because D doesn't provide any way to separate the stack-frame pointer from the function pointer. However, this seems like it should be possible since the function-pointer part of the delegate is commonly a compile-time constant. And if we could do that and the body of the loop was short, then it could actually be inlined which might speed this code up quite a bit.
Is there any way to do this? Does the D compiler have some trick by which it happens automagically?
Related
Note: I initially posted an over-simplified version of my problem. A more
accurate description follows:
I have the following struct:
struct Thing(T) {
T[3] values;
int opApply(scope int delegate(size_t, ref T) dg) {
int res = 0;
foreach(idx, ref val; values) {
res = dg(idx, val);
if (res) break;
}
return res;
}
}
Foreach can be used like so:
unittest {
Thing!(size_t[]) thing;
foreach(i, ref val ; thing) val ~= i;
}
However, it is not #nogc friendly:
#nogc unittest {
Thing!size_t thing;
foreach(i, ref val ; thing) val = i;
}
If I change the signature to
int opApply(scope int delegate(size_t, ref T) #nogc dg) { ... }
It works for the #nogc case, but fails to compile for non-#nogc cases.
The solutions I have tried are:
Cast the delegate
int opApply(scope int delegate(size_t, ref T) dg) {
auto callme = cast(int delegate(size_t, ref T) #nogc) dg;
// use callme instead of dg to support nogc
This seems wrong as I am willfully casting a #nogc attribute even onto
functions that do may not support it.
Use opSlice instead of opApply:
I'm not sure how to return an (index, ref value) tuple from my range. Even if
I could, I think it would have to contain a pointer to my static array, which
could have a shorter lifetime than the returned range.
Use a templated opApply:
All attempts to work with this have failed to automatically determine the
foreach argument types. For example, I needed to specify:
foreach(size_t idx, ref int value ; thing)
Which I see as a significant hindrance to the API.
Sorry for underspecifying my problem before. For total transparency,
Enumap is the "real-world" example. It
currently uses opSlice, which does not support ref access to values. My
attempts to support 'foreach with ref' while maintaining #nogc support is what
prompted this question.
Instead of overloading the opApplyoperator you can implement an input range for your type. Input ranges work automatically as the agregate argument in foreach statements:
struct Thing(K,V) {
import std.typecons;
#nogc bool empty(){return true;}
#nogc auto front(){return tuple(K.init, V.init);}
#nogc void popFront(){}
}
unittest {
Thing!(int, int) w;
foreach(val ; w) {
int[] i = [1,2,3]; // spurious allocation
}
}
#nogc unittest {
Thing!(int, int) w;
foreach(idx, val ; w) { assert(idx == val); }
}
This solves the problem caused by the allocation of the delegate used in foreach.
Note that the example is shitty (the range doesn't work at all, and usually ranges are provided via opSlice, etc) but you should get the idea.
I have the following range:
struct Range {
uint data;
#property{
bool empty() { return false; }
uint front() { return data; }
void popFront() { data = data * 2 + 1; }
}
}
Trying to use it,
foreach(c; Rnage()){ /*...*/ } works, but with foreach(i, c; Range()){ /*...*/ } I get:
Error: cannot infer argument types
I need the i just like in something like foreach(i, v; [1,2,3,4]){ }.
Ranges do not support the syntax
foreach(i, c; range)
While it seems obvious that that should work in the simple case, what that index should even be depends on the type of range and doesn't always make sense. So, no counter for the index is provided automatically by foreach, and a range has no way of providing one.
However, thanks to tuple unpacking with foreach, you can do it by using std.range.sequence std.range.zip with your range:
foreach (i, e; zip(sequence!"n"(), range))
{
}
By the way, you shouldn't mark popFront with #property. It doesn't make any sense. popFront takes no arguments and returns no value. It does not act like a variable at all. And the point of properties is to have functions which act like variables. If/when -property's implementation is fully sorted out and it becomes the normal behavior (it's rather buggy at the moment, which is part of why it's a separate switch for the moment), popFront would not be usable as you defined it.
If you use opApply to implement the range, You can overload one version for the without-index style and for the with-index style:
struct Range {
int opApply(int delegate(int) action){
uint data=0;
while(true){
action(data);
data=data*2+1;
}
return 0;
}
int opApply(int delegate(uint,int) action){
uint i=0;
foreach(element;this){
action(i++,element);
}
return 0;
}
}
I'm trying Lua and want to know how lua_State working
code and result:
state.c
#include <stdio.h>
#include "lua/src/lua.h"
#include "lua/src/lauxlib.h"
static void stackDump(lua_State *L){
int i;
int top = lua_gettop(L);
for(i = 1; i<= top; i++) {
int t = lua_type(L, i);
switch(t){
case LUA_TSTRING:
printf("'%s'", lua_tostring(L, i));
break;
case LUA_TBOOLEAN:
printf(lua_toboolean(L, i) ?"true":"false");
break;
case LUA_TNUMBER:
printf("%g", lua_tonumber(L, i));
break;
default:
printf("%s", lua_typename(L, t));
break;
}
printf(" ");
}
printf("\n");
}
static int divide(struct lua_State *L){
double a = lua_tonumber(L, 1);
double b = lua_tonumber(L, 2);
printf("%p\n", L);
stackDump(L);
int quot = (int)a / (int)b;
int rem = (int)a % (int)b;
lua_pushnumber(L, quot);
lua_pushnumber(L, rem);
stackDump(L);
printf("---end div---\n");
return 2;
}
int main(void){
struct lua_State *L = lua_open();
lua_pushboolean(L, 1);
lua_pushnumber(L, 10);
lua_pushnil(L);
lua_pushstring(L, "hello");
printf("%p\n", L);
stackDump(L);
lua_register(L, "div", divide);
luaL_dofile(L, "div.lua");
stackDump(L);
lua_close(L);
return 0;
}
div.lua
local c = div(20, 10)
0x100c009e0
true 10 nil 'hello'
---start div---
0x100c009e0
20 10
20 10 2 0
---end div---
true 10 nil 'hello'
I see lua_State in divide is the same with the main one, but they have different data in stack, How this be done ?
I know the best way to understand this is to read source code of Lua , maybe you can tell me where to find the right place.
Think of lua_State as containing the Lua stack, as well as indices delimiting the current visible part of the stack. When you invoke a Lua function, it may look like you have a new stack, but really only the indices have changed. That's the simplified version.
lua_State is defined in lstate.h. I've pulled out the relevant parts for you. stack is the beginning of the big Lua stack containing everything. base is the beginning of the stack for the current function. This is what your function sees as "the stack" when it is executing.
struct lua_State {
/* ... */
StkId top; /* first free slot in the stack */
StkId base; /* base of current function */
/* ... */
StkId stack_last; /* last free slot in the stack */
StkId stack; /* stack base */
/* ... */
};
Programming in Lua, 2nd Edition discusses Lua states in chapter 30: Threads and States. You'll find some good information there. For example, lua_State not only represents a Lua state, but also a thread within that state. Furthermore, all threads have their own stack.
It gets different data the same way anything gets different data: code changes the data inside of the object.
struct Object
{
int val;
};
void more_stuff(Object *the_data)
{
//the_data->val has 5 in it now.
}
void do_stuff(Object *the_data)
{
int old_val = the_data->val;
the_data->val = 5;
more_stuff(the_data);
the_data->val = old_val;
}
int main()
{
Object my_data;
my_data.val = 1;
//my_data.val has 1.
do_stuff(&my_data);
//my_data.val still has 1.
}
When Lua calls a registered C function, it gives it a new stack frame.
Here is my code:
struct S {
int a, b;
float c, d;
};
class A {
private:
S* d;
S h[3];
public:
A() {
cutilSafeCall(cudaMalloc((void**)&d, sizeof(S)*3));
}
void Init();
};
void A::Init() {
for (int i=0;i<3;i++) {
h[i].a = 0;
h[i].b = 1;
h[i].c = 2;
h[i].d = 3;
}
cutilSafeCall(cudaMemcpy(d, h, 3*sizeof(S), cudaMemcpyHostToDevice));
}
A a;
In fact it is a complex program which contain CUDA and OpenGL. When I debug this program, it fails when running at cudaMemcpy with the error information
cudaSafeCall() Runtime API error 11: invalid argument.
Actually, this program is transformed from another one that can run correctly. But in that one, I used two variables S* d and S h[3] in the main function instead of in the class. What is more weird is that I implement this class A in a small program, it works fine.
And I've updated my driver, error still exists.
Could anyone give me a hint on why this happen and how to solve it. Thanks.
Because the memory operations in CUDA are blocking, they make a synchronization point. So other errors, if not checked with cudaThreadSynchonize, will seem like errors on the memory calls.
So if an error is received on a memory operation, try to place a cudaThreadSynchronize before it and check the result.
Be sure that the first malloc statement is being executed. If it is a problem about initialization of CUDA, like #Harrism indicate, then it would fail in this statement?? Try to place printf statements, and see proper initializations are performed. I think generally invalid argument errors are generated because of using uninitalized memory areas.
Write a printf to your constructor showing the address of the cudaMalloc'ed memory area
A()
{
d = NULL;
cutilSafeCall(cudaMalloc((void**)&d, sizeof(S)*3));
printf("D: %p\n", d);
}
Try to make a memory copy for an area that is locally allocated, namely move the cudaMalloc to above of cudaMemcopy (just for testing).
void A::Init()
{
for (int i=0;i<3;i++)
{
h[i].a = 0;
h[i].b = 1;
h[i].c = 2;
h[i].d = 3;
}
cutilSafeCall(cudaMalloc((void**)&d, sizeof(S)*3)); // here!..
cutilSafeCall(cudaMemcpy(d, h, 3*sizeof(S), cudaMemcpyHostToDevice));
}
Good luck.
Does Dart support the concept of variable functions/methods? So to call a method by its name stored in a variable.
For example in PHP this can be done not only for methods:
// With functions...
function foo()
{
echo 'Running foo...';
}
$function = 'foo';
$function();
// With classes...
public static function factory($view)
{
$class = 'View_' . ucfirst($view);
return new $class();
}
I did not found it in the language tour or API. Are others ways to do something like this?
To store the name of a function in variable and call it later you will have to wait until reflection arrives in Dart (or get creative with noSuchMethod). You can however store functions directly in variables like in JavaScript
main() {
var f = (String s) => print(s);
f("hello world");
}
and even inline them, which come in handy if you are doing recusion:
main() {
g(int i) {
if(i > 0) {
print("$i is larger than zero");
g(i-1);
} else {
print("zero or negative");
}
}
g(10);
}
The functions stored can then be passed around to other functions
main() {
var function;
function = (String s) => print(s);
doWork(function);
}
doWork(f(String s)) {
f("hello world");
}
I may not be the best explainer but you may consider this example to have a wider scope of the assigning functions to a variable and also using a closure function as a parameter of a function.
void main() {
// a closure function assigned to a variable.
var fun = (int) => (int * 2);
// a variable which is assigned with the function which is written below
var newFuncResult = newFunc(9, fun);
print(x); // Output: 27
}
//Below is a function with two parameter (1st one as int) (2nd as a closure function)
int newFunc(int a, fun) {
int x = a;
int y = fun(x);
return x + y;
}