Merge pull request #391 from gdziadkiewicz/gdziadkiewicz/issue313

Add Option.someIf and tests for it.

paket.dependencies

@@ -23,6 +23,7 @@ group Test
   nuget NUnit
   nuget NUnit3TestAdapter
   nuget FsCheck
+  nuget FsCheck.NUnit
   nuget FsUnit
   nuget Microsoft.NET.Test.Sdk
   nuget Appveyor.TestLogger

paket.lock

@@ -708,6 +708,9 @@ NUGET
     Appveyor.TestLogger (2.0)
     FsCheck (2.14.2)
       FSharp.Core (>= 4.2.3)
+    FsCheck.NUnit (2.14.2)
+      FsCheck (2.14.2)
+      NUnit (>= 3.10.1 < 4.0)
     FSharp.Core (4.7.2)
     FsUnit (3.8.1)
       FSharp.Core (>= 4.2.3)

src/FSharpx.Extras/ComputationExpressions/Option.fs

@@ -242,4 +242,7 @@ module Option =
     let inline isSome (o:Option<'a>) : bool =
         match o with
         | Some _ -> true
-        | _ -> false
+        | _ -> false
+
+    /// Checks condition on x - if true returns Some x else None
+    let someIf (condition:'a->bool) (x:'a) : 'a option = if condition x then Some x else None

tests/FSharpx.Tests/FSharpx.Tests.fsproj

@@ -5,6 +5,7 @@
     <TargetFrameworks>net46;netcoreapp31</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
+    <LangVersion>preview</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' ">
     <TargetFrameworks>netcoreapp31</TargetFrameworks>

tests/FSharpx.Tests/OptionTests.fs

@@ -2,6 +2,8 @@
 
 open System
 open NUnit.Framework
+open FsUnitTyped
+open FsCheck.NUnit
 open FSharpx.Functional
 open FSharpx
 open FSharpx.Option
@@ -75,4 +77,20 @@ let ``orElseLazy Some``() =
 [<Test>]
 let ``orElseLazy None``() =
     let r = None |> Option.orElseLazy (lazy Some 2)
-    Assert.AreEqual(Some 2, r)
+    Assert.AreEqual(Some 2, r)
+
+[<Property>]
+let ``someIf with always true predicate`` (x:int) =
+    Option.someIf (konst true) x = Some x
+
+[<Property>]
+let ``someIf with always false predicate`` (x:int) =
+    Option.someIf (konst false) x = None
+
+let someIfBoolTestCases = [
+        TestCaseData(true, Some true)
+        TestCaseData(false, None)
+    ]
+[<TestCaseSource(nameof someIfBoolTestCases)>]
+let ``someIf with id`` (input:bool, expectedOutput:bool option) =
+    Option.someIf id input |> shouldEqual expectedOutput

tests/FSharpx.Tests/paket.references

@@ -1,6 +1,7 @@
 group Test
     FsCheck
     FsUnit
+    FsCheck.NUnit
     NUnit
     Microsoft.NET.Test.Sdk
     NUnit3TestAdapter