The below snippet of code gives me error in dartpad. But the same code works fine in the course which I am doing online. I am using dart version 2.8.4.
void main() {
int var = operation(5,5,add); --> Error
//print(operation(5,5,add));
}
// class calculator {
// calculator({this.operand});
// }
int add(int n1, int n2) {
return n1+n2;
}
int multiply(int n1, int n2) {
return n1*n2;
}
int operation(int n1, int n2, Function operand){
return operand(n1, n2);
}
Error:
Error compiling to JavaScript:
main.dart:3:2:
Error: Expected ';' after this.
int var = operation(5,5,add);
^^^
main.dart:3:10:
Error: Expected an identifier, but got '='.
int var = operation(5,5,add);
^
Error: Compilation failed.
int var = operation(5,5,add); don't use var as a variable name, it a keyword used in the dartlang, just change the name to anything else and you wont get any error:
int operationResult = operation(5,5,add);
Related
I am trying to implement a TSortedMap with my custom struct as the key. I have overloaded the operators for the struct. However, when I try to compile I get this error at the line of code where I am adding an element to the TSortedMap:
error C2678: binary '<': no operator found which takes a left-hand operand of type 'const T'
(or there is no acceptable conversion)
My struct:
USTRUCT(BlueprintType)
struct FUtility
{
GENERATED_BODY()
public:
UPROPERTY(BlueprintReadWrite, EditAnywhere, meta=(ClampMin = "0.0", ClampMax = "1.0"))
float value = 0.0f;
UPROPERTY(BlueprintReadWrite, EditAnywhere, meta = (ClampMin = "0.0", ClampMax = "1.0"))
float weight = 1.0f;
FORCEINLINE bool operator== (const FUtility& other)
{
return this->value == other.value && this->weight == other.weight;
}
FORCEINLINE bool operator< (const FUtility& other)
{
return (this->value * this->weight) < (other.value * other.weight);
}
.....
friend uint32 GetTypeHash(const FUtility& other)
{
return GetTypeHash(other.value) + GetTypeHash(other.weight);
}
};
Not quite sure why it is not compiling since it is overloaded. Maybe it isn't overloaded correctly. Any help would be greatly appreciated.
Well, oddly enough I figured it out. It was really bugging me that all of the operator logic in the documentation took two parameters. It turns out I was just missing the friend keyword. From there I was able to add the second parameter and it compiled nicely.
Example:
friend bool operator< (const FUtility& a, const FUtility& b)
{
return (a.value * a.weight) < (b.value * b.weight);
}
I tried to send a Map to a compute, but computer is never called. The strange point is if I replace Map with int, it works:
void A()
{
var map=Map();
map["p1"]=90;
D("before compute");
var r1 = await compute(p1, 10);
D("after compute(p1) : $r1");
var r2 = await compute(p2, map);
// code never reaches here!
D("after compute(p2) : $r2");
}
static int p2(Map p)
{
return p["p1"]*10;
}
static int p1(int z)
{
return z*10;
}
output is :
after compute(p1) : 100
Flutter compute methods use Isolates and its only transfer (null, num, bool, double, String) types.
https://api.flutter.dev/flutter/dart-isolate/SendPort/send.html
Just define exact type of Map that "p2" receives as parameter:
static int p2(Map<String,int> p)
{
return p["p1"]*10;
}
Try passing a const parameter:
var r2 = await compute(p2, {"p1":90});
I was just trying Apache Thrift in nodejs before using it in my upcoming project wherein I ran into this error.
Here is my demo.thrift file
namespace js demo
typedef i32 int
enum Operation {
ADD = 1,
SUBTRACT = 2,
MULTIPLY = 3,
DIVIDE = 4
}
struct Work {
1: int num1 = 0,
2: int num2,
3: Operation op,
4: optional string comment
}
exception InvalidOperation {
1: int message,
2: string trace
}
service Calculator {
void ping()
double calculate(1: int logid, 2: Work w) throws (1: InvalidOperation oops),
oneway void zip()
}
Here is a part of the server.js
I use switch case to determine operation in server.js
// inside thrift.createServer
calculate: (logid, work, result) => {
let answer = null, oops = null;
switch(work.op) {
// Code related to Operation.ADD, Operation.SUBTRACT ...
default: {
console.log("ERROR!");
oops = InvalidOperation();
oops.message = work.op;
oops.trace = "Unknown Operation";
}
}
result(oops, answer);
}
When the client.js calls server with calculate(12345, { num1:1, num2:2, op: 10 })
Instead of returning an error it throws
TypeError: Cannot set property 'name' of undefined in demo_types.js:122
The part related to InvalidOperation in demo_types.js is
// Work related code
var InvalidOperation = module.exports.InvalidOperation = function(args) {
Thrift.TException.call(this, "InvalidOperation");
this.name = "InvalidOperation"; // points to here
this.message = null;
this.trace = null;
if (args) {
if (args.message !== undefined && args.message !== null) {
this.message = args.message;
}
if (args.trace !== undefined && args.trace !== null) {
this.trace = args.trace;
}
}
};
Thrift.inherits(InvalidOperation, Thrift.TException);
InvalidOperation.prototype.name = 'InvalidOperation';
// InvalidOperation.read & .write
Any idea why the error is being thrown?
Actually I realised why this error is being thrown. It is a plain old Javascript mistake.
oops = new InvalidOperation();
That's it.
Code
BOOL CGrAllObjects::ReorderObj(CGrObject* pGrFind,int ixObjNewIx)
{
int nSubCode,nLyrCode=pGrFind->GetLayerCode(nSubCode);
CGrObject* pGrObject;
CGrObjectArray*
pGrObjectArray=GetObjArrayFromCode(nLyrCode,nSubCode);
if(!pGrObjectArray) return FALSE;
for(int ixObj=pGrObjectArray->GetSize()-1; ixObj>=0; ixObj--)
{ pGrObject=pGrObjectArray->GetAt(ixObj);
if(pGrObject==pGrFind) break;
}
if(ixObj<0) return FALSE;
if(ixObj!=ixObjNewIx)
{ pGrObjectArray->RemoveAt(ixObj);
pGrObjectArray->InsertAt(ixObjNewIx,pGrFind);
}
return TRUE;
}
Error: 1>c:\xxx\xxx\xxxx\xxxx\xxxx\xxxxx\xxxx.cpp(359) : error C2065:
'ixObj' : undeclared identifier
for(int ixObj ... the variable "ixObj" is only defined in the scope of the for loop and is not known outside.
Define the integer before the loop, and remove the decalration from 'for':
int ixObj;
for(ixObj=...
Haxe seems to assume that certain things must be Int. In the following function,
class Main {
static function main() {
function mult_s<T,A>(s:T,x:A):A { return cast s*x; }
var bb = mult_s(1.1,2.2);
}
}
I got (with Haxe 3.01):
Main.hx:xx: characters 48-49 : mult_s.T should be Int
Main.hx:xx: characters 50-51 : mult_s.A should be Int
Can anyone please explain why T and A should be Int instead of Float?
A more puzzling example is this:
class Main {
public static function min<T:(Int,Float)>(t:T, t2:T):T { return t < t2 ? t : t2; }
static function main() {
var a = min(1.1,2.2); //compile error
var b = min(1,2); //ok
}
}
I can't see why t<t2 implies that either t or t2 is Int. But Haxe seems prefer Int: min is fine if called with Int's but fails if called with Float's. Is this reasonable?
Thanks,
min<T:(Int,Float)> means T should be both Int and Float. See the constraints section of Haxe Manual.
Given Int can be converted to Float implicitly, you can safely remove the constraint of Int. i.e. the following will works:
http://try.haxe.org/#420bC
class Test {
public static function min<T:Float>(t:T, t2:T):T { return t < t2 ? t : t2; }
static function main() {
var a = min(1.1,2.2); //ok
$type(a); //Float
trace(a); //1.1
var b = min(1,2); //ok
$type(b); //Int
trace(b); //1
}
}