Create an object at a given address: Difference between revisions
Create an object at a given address (view source)
Revision as of 11:03, 10 October 2021
, 2 years agoAdded Wren
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var 'bar' at 19363848 with value 0
incremented 'foo' so 'bar' is 1</pre>
=={{header|Wren}}==
{{libheader|Wren-fmt}}
Wren is a high-level scripting language which doesn't support pointers and has no way of obtaining the machine address of variables.
This is still true even when Wren is embedded in a program written in a low-level language such as C because the embedding API has been designed so as not to expose raw pointers to memory managed by Wren to the host.
Perhaps the closest we can get to the spirit of this task is to create a new ''foreign'' class, ''Integer'', memory for which is allocated from a C host and the machine address is therefore available. We can then use this class to wrap Wren integers (though, strictly speaking, Wren doesn't have integers - they're just a special case of the ''Num'' class), get and set their values and take their address.
Note that it is not possible to specify the address at which the embedding API function ''wrenSetSlotNewForeign'' allocates new objects and any attempt to allocate a new object at the same address as an old one by juggling with pointers will almost certainly lead to a seg fault. So all we can sensibly do is to change the value of the current object.
<lang ecmascript>/* create_object_at_given_address.wren */
import "./fmt" for Fmt
foreign class Integer {
construct new(i) {}
foreign value
foreign value=(i)
foreign address
}
var i = Integer.new(42)
Fmt.print("Integer object with value of: $d allocated at address $#x.", i.value, i.address)
i.value = 42
Fmt.print("Integer object value reset to: $d but still at address $#x.", i.value, i.address)
i.value = 43
Fmt.print("Integer object value changed to: $d but still at address $#x.", i.value, i.address)</lang>
<br>
We now embed this in the following C program, compile and run it.
<lang c>/* gcc create_object_at_given_address.c -o create_object_at_given_address -lwren -lm */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "wren.h"
/* C <=> Wren interface functions */
void C_integerAllocate(WrenVM* vm) {
long *pi = (long *)wrenSetSlotNewForeign(vm, 0, 0, sizeof(long));
long i = (long)wrenGetSlotDouble(vm, 1);
*pi = i;
}
void C_value(WrenVM* vm) {
long i = *(long *)wrenGetSlotForeign(vm, 0);
wrenSetSlotDouble(vm, 0, (double)i);
}
void C_setValue(WrenVM* vm) {
long *pi = (long *)wrenGetSlotForeign(vm, 0);
long i = (long)wrenGetSlotDouble(vm, 1);
*pi = i;
}
void C_address(WrenVM* vm) {
long *pi = (long *)wrenGetSlotForeign(vm, 0);
wrenSetSlotDouble(vm, 0, (double)(unsigned long long)pi);
}
WrenForeignClassMethods bindForeignClass(WrenVM* vm, const char* module, const char* className) {
WrenForeignClassMethods methods;
methods.allocate = NULL;
methods.finalize = NULL;
if (strcmp(module, "main") == 0) {
if (strcmp(className, "Integer") == 0) {
methods.allocate = C_integerAllocate;
}
}
return methods;
}
WrenForeignMethodFn bindForeignMethod(
WrenVM* vm,
const char* module,
const char* className,
bool isStatic,
const char* signature) {
if (strcmp(module, "main") == 0) {
if (strcmp(className, "Integer") == 0) {
if (!isStatic && strcmp(signature, "value") == 0) return C_value;
if (!isStatic && strcmp(signature, "value=(_)") == 0) return C_setValue;
if (!isStatic && strcmp(signature, "address") == 0) return C_address;
}
}
return NULL;
}
static void writeFn(WrenVM* vm, const char* text) {
printf("%s", text);
}
void errorFn(WrenVM* vm, WrenErrorType errorType, const char* module, const int line, const char* msg) {
switch (errorType) {
case WREN_ERROR_COMPILE:
printf("[%s line %d] [Error] %s\n", module, line, msg);
break;
case WREN_ERROR_STACK_TRACE:
printf("[%s line %d] in %s\n", module, line, msg);
break;
case WREN_ERROR_RUNTIME:
printf("[Runtime Error] %s\n", msg);
break;
}
}
char *readFile(const char *fileName) {
FILE *f = fopen(fileName, "r");
fseek(f, 0, SEEK_END);
long fsize = ftell(f);
rewind(f);
char *script = malloc(fsize + 1);
fread(script, 1, fsize, f);
fclose(f);
script[fsize] = 0;
return script;
}
static void loadModuleComplete(WrenVM* vm, const char* module, WrenLoadModuleResult result) {
if( result.source) free((void*)result.source);
}
WrenLoadModuleResult loadModule(WrenVM* vm, const char* name) {
WrenLoadModuleResult result = {0};
if (strcmp(name, "random") != 0 && strcmp(name, "meta") != 0) {
result.onComplete = loadModuleComplete;
char fullName[strlen(name) + 6];
strcpy(fullName, name);
strcat(fullName, ".wren");
result.source = readFile(fullName);
}
return result;
}
int main(int argc, char **argv) {
WrenConfiguration config;
wrenInitConfiguration(&config);
config.writeFn = &writeFn;
config.errorFn = &errorFn;
config.bindForeignClassFn = &bindForeignClass;
config.bindForeignMethodFn = &bindForeignMethod;
config.loadModuleFn = &loadModule;
WrenVM* vm = wrenNewVM(&config);
const char* module = "main";
const char* fileName = "create_object_at_given_address.wren";
char *script = readFile(fileName);
WrenInterpretResult result = wrenInterpret(vm, module, script);
switch (result) {
case WREN_RESULT_COMPILE_ERROR:
printf("Compile Error!\n");
break;
case WREN_RESULT_RUNTIME_ERROR:
printf("Runtime Error!\n");
break;
case WREN_RESULT_SUCCESS:
break;
}
wrenFreeVM(vm);
free(script);
return 0;
}</lang>
{{out}}
Sample output:
<pre>
Integer object with value of: 42 allocated at address 0x55a56e0f2dd8.
Integer object value reset to: 42 but still at address 0x55a56e0f2dd8.
Integer object value changed to: 43 but still at address 0x55a56e0f2dd8.
</pre>
{{omit from|AWK}}
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