In freemarker, can you assign a boolean value like this:
[#if something = value]
[#assign bool = true]
[/#if]
To then be used in a conditional statement like this:
[#if bool]
...do something
[/#if]
So far I have not been successful doing this in this format, but thought I might be missing something. Do i need to declare the variable outside the first if statement to keep it in scope and reuse later?
You haven't included the error message... but I guess your problem is that if the first condition is false, then you never assign to the bool variable, so it won't exist at all, and so you can't use it in the second expression. To fix that, the first #if could to be changed to:
[#assign bool = something == value]
Related
With arrays you can use a subscript to access Array Elements directly. You can read or write to them. With Sets I am not sure of a way to write its Elements.
For example, if I access a set element matching a condition I'm only able to read the element. It is passed by copy and I can't therefore write to the original.
For example:
columns.first(
where: {
$0.header.last == Character(String(i))
}
)?.cells.append(value: addValue)
// ERROR: Cannot use mutating member on immutable value: function call returns immutable value
You can't just change things inside a set, because of how a (hash) set works. Changing them would possibly change their hash value, making the set into an invalid state.
Therefore, you would have to take the thing you want to change out of the set, change it, then put it back.
if var thing = columns.first(
where: {
$0.header.last == Character(String(i))
}) {
columns.remove(thing)
thing.cells.append(value: addValue)
columns.insert(thing)
}
If the == operator on Column doesn't care about cells (i.e. adding cells to a column doesn't suddenly make two originally equal columns unequal and vice versa), then you could use update instead:
if var thing = columns.first(
where: {
$0.header.last == Character(String(i))
}) {
thing.cells.append(value: addValue)
columns.update(thing)
}
As you can see, it's quite a lot of work, so maybe sets aren't a suitable data structure to use in this situation. Have you considered using an array instead? :)
private var _columns: [Column]
public var columns : [Column] {
get { _columns }
set { _columns = Array(Set(newValue)) }
// or any other way to remove duplicate as described here: https://stackoverflow.com/questions/25738817/removing-duplicate-elements-from-an-array-in-swift
}
You are getting the error because columns might be a set of struct. So columns.first will give you an immutable value. If you were to use a class, you will get a mutable result from columns.first and your code will work as expected.
Otherwise, you will have to do as explained by #Sweeper in his answer.
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 just wanted to know what does this code do?
my $string_1 = "foo bar";
my $val = 3;
if($string_1) {
}
basically what happen if you just use a variable inside an if statement?
thanks
It checks if the value of the variable is true. In Perl, everything is true but the following:
0 and the string '0'
undef
() (the empty list)
'' (an empty string)
This is documented in perlsyn. It also works with any other kind of value. You can also put a string, a function call inside the if condition. The behavior is always the same.
this will check variable '$string' has not null value
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;
}
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
}