Can I do ternary in the postlude(s) the same way that I do them int he prelude? In other words have it fire off different calls depending on the say something was evaluated in the prelude?
Yes. You can include a guard condition on a postlude expression. This works for both explicit event raising and persistant variable modification. The expression following if can be any valid expression, including functions.
Example:
fired {
raise explicit event "foo" if cheese == 5;
}
Related
I want to feed Two to the function. When function receives Two as the data, it should print success to the console. But seems like it's not the correct way.
Error: Conditions must have a static type of 'bool'. Try changing the condition.
List
enum ButtonList {One, Two, Three}
Calling function
testFunc(ButtonList.Two)),
Function
testFunc( ButtonList type) {
if (type = ButtonList.Two ){print('sucess ')};
}
It should be:
testFunc(ButtonList type) {
if (type == ButtonList.Two) {
print('sucess ')
};
}
There's a big difference between = (assigning a value to a variable) and == (equality comparison). if expects a condition (==), not the assigning operation (=).
Formatting is important to read and understand the code. Please read Dart best code style practices: https://dart.dev/guides/language/effective-dart/style
You are trying to assign with =, use == instead
I know that in the latest version of dart we can use if else statements inside the build method. Does anyone know if we can use also if else statement when we setting class parameters? I know I can do inline statement there but inline is a bit hard to read when there are multiple conditions
const int i = 0;
class Person {
// NewClass n = NewClass(a: i == 0 ? 'a' : 'b'); //<- inline statement working
NewClass n = NewClass(a: if(i == 0) 'a' else 'b'); //<- if statement doesn't
}
class NewClass {
final String a;
const NewClass({this.a});
}
Edit:
Basically in my case I've got an TextField widget where I set its's type parameter from enum (Type.text, Type.numeric...) According to this parameter I want to set The textField parameters (textCapitalization, maxLength and so on)
As per your comment, you are already creating an enum for specifying the type of the fields.
enum Type {text, numeric}
Now for specifying the properties of that particular type, you can add an extension on this enum, as shown below:
extension TextFieldProperties on Type {
int get maxLength {
if (this == Type.text) {
return 10;
}
return 12;
}
}
So in your field class you already have a type defined, you can use that type variable to get the properties of that particular type of field.
Type type = Type.text;
print(type.maxLength); // Will print 10
type = Type.numeric;
print(type.maxLength); // Will print 12
Note: It will work only in Dart 2.7 and above
You want the conditional expression (?:), not the conditional statement or literal entry (if), as you have already discovered.
The reason if doesn't work is that if only works as a statement or as a collection literal entry. It doesn't work in arbitrary expressions.
The reason for the distinction is that the if syntax allows you to omit the else branch. That only makes sense in places where "nothing" is a valid alternative. For a statement, "doing nothing" is fine. For a collection, "adding nothing" is also fine.
In an expression context, you must evaluate to a value or throw. There is no reasonable default that we can use instead of "nothing", so an if is not allowed instead of an expression.
Doesn't work because this syntax doesn't exist in Dart. The only way to do what you would like to do is to use the ternary operator.
If you try it in the DartPad you will get an error.
I suggest you to use a function to return the right value.
I'm programming in Swift 5.0 an app to move my character around a world and I've some problems with the NOT (!) operator in the if condition body.
I wrote:
if character.!isBlocked {
character.moveForward()
}
but the compiler say: Error: ".!" it's not a binary operator
Instead, if I wrote
if character.isBlocked {
character.turnBack()
}
it works perfectly. Its possible to use a negative clause as if condition clause?
If you are aiming to validate as "if not", then you should implement it as:
if !character.isBlocked {
character.moveForward()
}
The logical NOT ! operator is a unary prefix operator:
Unary: it is for a single target.
Prefix: it should be before the target.
So, why it should be before character.isBlocked but not isBlocked?
Because character.isBlocked is the boolean to evaluate, isBlocked is the property name. The correct syntax is to use ! to evaluate the whole thing (Boolean value).
I'm working on a CDCL SAT-Solver. I don't know how to implement non-chronological backtracking. Is this even possible with recursion or is it only possible in a iterative approach.
Actually what i have done jet is implemented a DPLL Solver which works with recursion. The great differnece from DPLL and CDCL ist that the backracking in the tree is not chronological. Is it even possible to implement something like this with recursion. In my opionion i have two choices in the node of the binary-decision-tree if one of to path leads i a conlict:
I try the other path -> but then it would be the same like the DPLL, means a chronological backtracking
I return: But then i will never come back to this node.
So am i missing here something. Could it be that the only option is to implement it iterativly?
Non-chronological backtracking (or backjumping as it is usually called) can be implemented in solvers that use recursion for the variable assignments. In languages that support non-local gotos, you would typically use that method. For example in the C language you would use setjmp() to record a point in the stack and longjmp() to backjump to that point. C# has try-catch blocks, Lispy languages might have catch-throw, and so on.
If the language doesn't support non-local goto, then you can implement a substitute in your code. Instead of dpll() returning FALSE, have it return a tuple containing FALSE and the number of levels that need to be backtracked. Upstream callers decrement the counter in the tuple and return it until zero is returned.
You can modify this to get backjumping.
private Assignment recursiveBackJumpingSearch(CSP csp, Assignment assignment) {
Assignment result = null;
if (assignment.isComplete(csp.getVariables())) {
result = assignment;
}
else {
Variable var= selectUnassignedVariable(assignment, csp);
for (Object value : orderDomainValues(var, assignment, csp)) {
assignment.setAssignment(var, value);
fireStateChanged(assignment, csp);
if (assignment.isConsistent(csp.getConstraints(var))) {
result=recursiveBackJumpingSearch(csp, assignment);
if (result != null) {
break;
}
if (result == null)
numberOfBacktrack++;
}
assignment.removeAssignment(var);
}
}
return result;
}
I'm trying to write a class for a scala project and I get this error in multiple places with keywords such as class, def, while.
It happens in places like this:
var continue = true
while (continue) {
[..]
}
And I'm sure the error is not there since when I isolate that code in another class it doesn't give me any error.
Could you please give me a rule of thumb for such errors? Where should I find them? are there some common syntactic errors elsewhere when this happens?
It sounds like you're using reserved keywords as variable names. "Continue", for instance, is a Java keyword.
You probably don't have parentheses or braces matched somewhere, and the compiler can't tell until it hits a structure that looks like the one you showed.
The other possibility is that Scala sometimes has trouble distinguishing between the end of a statement with a new one on the next line, and a multi-line statement. In that case, just drop the ; at the end of the first line and see if the compiler's happy. (This doesn't seem like it fits your case, as Scala should be able to tell that nothing should come after true, and that you're done assigning a variable.)
Can you let us know what this code is inside? Scala expects "expressions" i.e. things that resolve to a particular value/type. In the case of "var continue = true", this does not evaluate to a value, so it cannot be at the end of an expression (i.e. inside an if-expression or match-expression or function block).
i.e.
def foo() = {
var continue = true
while (continue) {
[..]
}
}
This is a problem, as the function block is an expression and needs to have an (ignored?) return value, i.e.
def foo() = {
var continue = true
while (continue) {
[..]
}
()
}
() => a value representing the "Unit" type.
I get this error when I forget to put an = sign after a function definition:
def function(val: String):Boolean {
// Some stuff
}