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
3,818
questions
-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 ...
-2
votes
0
answers
36
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;@...
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 ...
- 1,034
-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::...
- 1
-3
votes
2
answers
242
views
Why does `emplace()` without arguments return 0 and can we use it to read a `std::optional<unsigned>` variable? [duplicate]
Is there a way to typecast an optional unsigned std::optional<unsigned> variable to unsigned?
#include <optional>
#include <iostream>
int main()
{
std::optional<unsigned> ...
- 306
1
vote
8
answers
137
views
Decent idiom for initializing an optional to either null or a value?
Motivation
With C++ having gotten optional's (in C++17), it is now common to want to write the equivalent of:
If a condition holds, initialize my variable with some expression; and if the condition ...
- 127k
0
votes
1
answer
92
views
Optional's orElse() executed even when object is present [duplicate]
I've encountered an unexpected behavior while using the Optional API in Java.
Session session = sessionService
.getSessionById(id)
.orElse(
...
- 119
1
vote
0
answers
22
views
Why Optional lambda replace with method reference Causing NullPointerException [duplicate]
There is a A Class
class A {
private String str;
public void setStr(String str) {
this.str = str;
}
}
this method works fine;
public static void main(String[] args) {
...
- 11
0
votes
0
answers
18
views
fetching rows from db that are selected by dropbar
guys i wrote a dropdown bar connected to a db, but i couldnt make the content of the table thats fetched from db only specified by the option i chose in drop bar, how can i fix this
here's my code:
$...
- 1
-1
votes
1
answer
92
views
How to force non-optional type (for array element) on compile time in Swift? [closed]
struct MyStruct {
@ArrayOfNonOptionalElements var arr: [SomeNonOptionalType]
}
where @ArrayOfNonOptionalElements is a propertyWrapper.
So, how to force non-optionality for the type inside? Is it ...
- 1,485
-1
votes
1
answer
122
views
Generate a type from a Java DTO type with many fields being null and have all getters as Optional<T>
I am currently working with a Java DTO class (written by others) that has almost 300 fields where many of these end up being null. What I see in the codebase are lots of null checks and more recently ...
- 528
-4
votes
2
answers
45
views
How to pass a positional argument from one function to *args in another function in python
I have a two scripts and a custom email module with two Functions that works.
But I need a single generic function in the custom email module used by both the scripts .
Script 1
import email_module....
- 1
0
votes
3
answers
71
views
Springboot: How to get an entity optional property and check null?
I have a service in Springboot and I want to get an optional entity and to check if is not null to do something after.
User repository class
public interface UserRepository extends JpaRepository<...
- 325
0
votes
1
answer
31
views
Typescript Maybe, error about null not being covered
I don't know how to get rid of this error, and I don't know why it talks about null.
Shouldn't the seo?.breadcrumbs || [] already cover the case where breadcrumbs is null?
However in the Intro Propos, ...
- 5,843
2
votes
2
answers
116
views
Optional.ifPresent throws NPE when action is null AND optional not present
Why does this throw a NullPointerException?
The docs for Java 8 state that:
"If a value is present, invoke the specified consumer with the value, otherwise do nothing."
public static ...
- 340