Questions tagged [option-type]
The option type or maybe type is a polymorphic type that represents encapsulation of an optional value where one side encapsulates the value, and other side represents the absence of the value (None, Nothing, etc). This tag is adequate for questions about `Option` in Scala, `Optional` in Java and Swift, `std::optional` in C++ and similar types.
option-type
3,822
questions
-4
votes
2
answers
250
views
Why `emplace()` without arguments returns 0 when I try to read an `std::optional<unsigned>` variable? [duplicate]
Below is the example code snippet:
#include <optional>
#include <iostream>
int main()
{
std::optional<unsigned> check = 200;
std::cout << check << std::endl;
...
- 304
0
votes
2
answers
1k
views
Bootstrap 5 is not working after I using Select2 dropdown
The Select2 functionality is functioning correctly. However, there is an issue with Bootstrap, after using Select2, Bootstrap is not working anymore. I am using Bootstrap 5.3.The picture show that the ...
- 439
-2
votes
0
answers
11
views
The automatic selection method of two drop-down fields linked together with JavaScript [closed]
When the site is reloaded, the drop-down boxes will be filled automatically
And after the first drop-down field is filled, the second drop-down field will be filled automatically
For example, the ...
3
votes
3
answers
795
views
Iterating over std::optional
I tried to iterate over an std::optional:
for (auto x : optionalValue)
{
...
}
With the expectation of it doing nothing if optionalValue is empty but doing one iteration if there is a value ...
- 3,032
-2
votes
0
answers
37
views
Why Java shows strange characters when print a OptionalDouble? [duplicate]
I declared a OptionalDouble vector, and when the program print this give me strange characters instead of the vector values:
[[Ljava.util.OptionalDouble;@37bba4006. [[Ljava.util.OptionalDouble;@...
168
votes
11
answers
205k
views
Default optional parameter in Swift function
When I set firstThing to default nil this will work, without the default value of nil I get a error that there is a missing parameter when calling the function.
By typing Int? I thought it made it ...
0
votes
2
answers
59
views
unwrap or evalulate to false in rust
I have encountered several cases similar this:
if let Some(x) = formula_chars.peek() {
if x.is_lowercase() {
todo!()
}
}
where I would like an expression to evaluate to false if an ...
- 65.5k
-4
votes
0
answers
75
views
std::optional is not available though I'm using G++9 [closed]
`error: ‘optional’ in namespace ‘std’ does not name a template type
** | std::optional<double> ;
| ^~~~~~~~
‘std::optional’ is only available from C++17 onwards
** | std::...
- 51.7k
667
votes
28
answers
332k
views
Why should Java 8's Optional not be used in arguments
I've read on many Web sites Optional should be used as a return type only, and not used in method arguments. I'm struggling to find a logical reason why. For example I have a piece of logic which ...
- 171
1
vote
2
answers
6k
views
JSON schema validation of optional fields using Golang
Golang JSON schema validation libraries validate that required fields on the schema are present in the service request/response.
I need to validate that any field in a service request or response ...
0
votes
1
answer
134
views
How to call an API and select correct optional from update method in spring MVC
I have been following online tutorials for MVC but have hit a snag with updating.
Have used a updateStudent() method in the controller and pass in the id, but inside the updateStudent() I have a lot ...
- 5,837
21
votes
2
answers
15k
views
How do I convert a list of Option<T> to a list of T when T cannot be copied? [duplicate]
How do I take a Vec<Option<T>>, where T cannot be copied, and unwrap all the Some values?
I run into an error in the map step. I'm happy to move ownership of the original list and "throw ...
- 296k
1
vote
1
answer
1k
views
Regex to match array of strings and optional array of strings
I am making a syntax highlighting service for guitar chord sheets. I am trying to highlight the guitar chords and not the lyrics. However, it gets complicated when guitar chords can be comprised of ...
- 249k
182
votes
6
answers
88k
views
Swift optional escaping closure parameter
Given:
typealias Action = () -> ()
var action: Action = { }
func doStuff(stuff: String, completion: @escaping Action) {
print(stuff)
action = completion
completion()
}
func ...
- 485
14
votes
2
answers
11k
views
How to safely unwrap optional variables in dart?
I couldn't find a way to safely unwrap an optional variable as we do in swift
var myString: String?
if let myString = myString {
print(myString) // myString is a string
}
or in Kotlin
var myString: ...
- 5,764