All Questions
Tagged with optional or option-type
3,832 questions
0
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161
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Passing nullable struct into view in SwiftUI [duplicate]
Note that I do not agree that my question is a duplicate of the linked question, even though the title would appear to imply it is. The accepted answer to that question is to force unwrap Binding<...
- 7,637
3
votes
1
answer
100
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Why is the getOrElse() function of arrow-kt returning Any?
I am trying to understand the getOrElse() function of arrow-kt. I want to create a simple function that takes a list of strings, filters them, and returns the first matching value as an Option<...
- 1,849
1
vote
1
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105
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Replacing Arrow's deprecated orElse with getOrElse doesn't work
I'm working on migrating some existing Kotlin code from Arrow 1.x to 2.x. The old code looked something like this:
fun filterStrings(incoming: List<String>): Option<String> = incoming
....
- 1,849
0
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2
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239
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How is Maybe a monad in Haskell?
A monad, I've been told, is a monoid of X in the category of endofunctors of X, where X is some category.
Maybe is supposedly then a monoid, which means that it is: an object of a category, some ...
- 19
1
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2
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85
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`Option.defaultValue` not working properly in f# when raising exception
I am trying to combine Option.defaultValue with failWith to get exception for None values:
printf "%A" (Some 1 |> Option.defaultValue (failwith "Error"))
But this code raise ...
- 6,659
7
votes
1
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108
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With &mut self, why can't this method move and replace a field's value?
I'm trying to implement a binary search tree. The parent struct, BinSearchTree, has a pointer to a root node:
pub struct BinSearchTree {
root: Option<Box<Node>>,
size: u32,
}
...
- 2,797
1
vote
1
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101
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How to downcast any List or any Option in rust
I want to add properties window with auto properties based on struct fields. I'am downcasting every field, but for Vec<> and Option<> I have to duplicate all code, how can I automatically ...
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2
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83
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conditional map fetch efficiently
I have a map which lays down prices of commodities in different currencies
val commpricemap: Map[String , Map[String, Double]] = ???
AN example of an entry for gold is as below:
("AU" -> ...
- 10k
1
vote
2
answers
101
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Filter an optional sequence
I have a Option sequence of dates - from which I need to SAFELY extract the first date after a given date( or else return the given date).
The below seems to be a lot of code for such a simple used ...
- 10k
1
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1
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148
views
I can't get an optional with (cond) ? value : nullopt ... what should I write instead?
Suppose I'm implementing the function returning an std::optional<T>. In that function, I compute some condition, and then want to return either a value, or a nullopt. I can do it like so:
std::...
- 140k
0
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1
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244
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How can I "merge" two options, keeping one if only one exists? [duplicate]
I find myself regularly encountering the need for logic where two optional values should be "merged" where:
if both are None -> give me None
if only one is Some -> give me Some of ...
- 66.2k
0
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1
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119
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In Standard ML, are datatype constructors considered values?
My working definition for value is a special kind of expression that evaluates to itself. So 1 is a value, and 1 + 1 is valuable but not a value because it evaluates to 2.
A datatype constructor like ...
- 11.7k
3
votes
2
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202
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Why doesn't MonadMaybe exist?
The way I look at MonadState, for instance, is that any type (or set of types, e.g. ReaderT r m a) that implements it, must support get+put (or alternatively just state) in order to behave like the ...
- 30.8k
3
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1
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84
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Why does Array's contains(_:) method cause an error when comparing an optional value with a non-optional value in Swift?
I’m working with Swift and encountered an issue when using the contains method on an array. The following code works fine:
let result = ["hello", "world"].contains(Optional("...
- 33
1
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4
answers
92
views
How can I find the only matching element in a Seq[A] as an Option[A], throwing an exception if there is more than one matching element?
In some test code, I have a Seq[A] that I'm filtering down to items matching a given property. There should be at most one such element in the sequence. If it has more, it means I set up something ...
- 23.7k
