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FlagsAttribute F# snippets (#7726)
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‎snippets/fsharp/System/FlagsAttribute/Overview/flags.fs

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module flags
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//<Snippet1>
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open System
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// Define an Enum without FlagsAttribute.
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type SingleHue =
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| None = 0
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| Black = 1
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| Red = 2
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| Green = 4
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| Blue = 8
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// Define an Enum with FlagsAttribute.
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[<Flags>]
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type MultiHue =
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| None = 0
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| Black = 1
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| Red = 2
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| Green = 4
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| Blue = 8
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// Display all possible combinations of values.
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printfn "All possible combinations of values without FlagsAttribute:"
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for i = 0 to 16 do
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printfn $"{i,3} - {enum<SingleHue> i:G}"
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// Display all combinations of values, and invalid values.
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printfn "\nAll possible combinations of values with FlagsAttribute:"
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for i = 0 to 16 do
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printfn $"{i,3} - {enum<MultiHue> i:G}"
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// The example displays the following output:
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// All possible combinations of values without FlagsAttribute:
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// 0 - None
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// 1 - Black
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// 2 - Red
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// 3 - 3
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// 4 - Green
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// 5 - 5
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// 6 - 6
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// 7 - 7
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// 8 - Blue
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// 9 - 9
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// 10 - 10
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// 11 - 11
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// 12 - 12
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// 13 - 13
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// 14 - 14
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// 15 - 15
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// 16 - 16
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//
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// All possible combinations of values with FlagsAttribute:
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// 0 - None
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// 1 - Black
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// 2 - Red
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// 3 - Black, Red
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// 4 - Green
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// 5 - Black, Green
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// 6 - Red, Green
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// 7 - Black, Red, Green
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// 8 - Blue
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// 9 - Black, Blue
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// 10 - Red, Blue
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// 11 - Black, Red, Blue
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// 12 - Green, Blue
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// 13 - Black, Green, Blue
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// 14 - Red, Green, Blue
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// 15 - Black, Red, Green, Blue
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// 16 - 16
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//</Snippet1>

‎snippets/fsharp/System/FlagsAttribute/Overview/flags1.fs

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module flags1
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// <Snippet2>
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open System
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[<Flags>]
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type PhoneService =
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| None = 0
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| LandLine = 1
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| Cell = 2
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| Fax = 4
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| Internet = 8
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| Other = 16
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// Define three variables representing the types of phone service
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// in three households.
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let household1 =
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PhoneService.LandLine ||| PhoneService.Cell ||| PhoneService.Internet
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let household2 =
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PhoneService.None
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let household3 =
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PhoneService.Cell ||| PhoneService.Internet
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// Store the variables in a list for ease of access.
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let households =
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[ household1; household2; household3 ]
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// Which households have no service?
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for i = 0 to households.Length - 1 do
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printfn $"""Household {i + 1} has phone service: {if households[i] = PhoneService.None then "No" else "Yes"}"""
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printfn ""
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// Which households have cell phone service?
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for i = 0 to households.Length - 1 do
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printfn $"""Household {i + 1} has cell phone service: {if households[i] &&& PhoneService.Cell = PhoneService.Cell then "Yes" else "No"}"""
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printfn ""
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// Which households have cell phones and land lines?
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let cellAndLand =
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PhoneService.Cell ||| PhoneService.LandLine
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for i = 0 to households.Length - 1 do
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printfn $"""Household {i + 1} has cell and land line service: {if households[i] &&& cellAndLand = cellAndLand then "Yes" else "No"}"""
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printfn ""
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// List all types of service of each household?//
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for i = 0 to households.Length - 1 do
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printfn $"Household {i + 1} has: {households[i]:G}"
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// The example displays the following output:
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// Household 1 has phone service: Yes
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// Household 2 has phone service: No
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// Household 3 has phone service: Yes
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//
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// Household 1 has cell phone service: Yes
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// Household 2 has cell phone service: No
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// Household 3 has cell phone service: Yes
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//
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// Household 1 has cell and land line service: Yes
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// Household 2 has cell and land line service: No
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// Household 3 has cell and land line service: No
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//
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// Household 1 has: LandLine, Cell, Internet
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// Household 2 has: None
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// Household 3 has: Cell, Internet
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// </Snippet2>

‎snippets/fsharp/System/FlagsAttribute/Overview/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="flags.fs" />
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<Compile Include="flags1.fs" />
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</ItemGroup>
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</Project>

‎xml/System/FlagsAttribute.xml

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:::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.FlagsAttribute/CPP/flags.cpp" id="Snippet1":::
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:::code language="csharp" source="~/snippets/csharp/System/FlagsAttribute/Overview/flags.cs" interactive="try-dotnet" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/FlagsAttribute/Overview/flags.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.FlagsAttribute/VB/flags.vb" id="Snippet1":::
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The preceding example defines two color-related enumerations, `SingleHue` and `MultiHue`. The latter has the `FlagsAttribute` attribute; the former does not. The example shows the difference in behavior when a range of integers, including integers that do not represent underlying values of the enumeration type, are cast to the enumeration type and their string representations displayed. For example, note that 3 cannot be represented as a `SingleHue` value because 3 is not the underlying value of any `SingleHue` member, whereas the `FlagsAttribute` attribute makes it possible to represent 3 as a `MultiHue` value of `Black, Red`.
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:::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.FlagsAttribute/CPP/flags1.cpp" id="Snippet2":::
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:::code language="csharp" source="~/snippets/csharp/System/FlagsAttribute/Overview/flags1.cs" interactive="try-dotnet" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/FlagsAttribute/Overview/flags1.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.FlagsAttribute/VB/flags1.vb" id="Snippet2":::
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]]></format>
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:::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.FlagsAttribute/CPP/flags1.cpp" id="Snippet2":::
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:::code language="csharp" source="~/snippets/csharp/System/FlagsAttribute/Overview/flags1.cs" interactive="try-dotnet" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/FlagsAttribute/Overview/flags1.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.FlagsAttribute/VB/flags1.vb" id="Snippet2":::
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The following example illustrates the use of the `FlagsAttribute` attribute and shows the effect on the <xref:System.Enum.ToString%2A> method of using `FlagsAttribute` on an <xref:System.Enum> declaration.
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:::code language="cpp" source="~/snippets/cpp/VS_Snippets_CLR_System/system.FlagsAttribute/CPP/flags.cpp" id="Snippet1":::
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:::code language="csharp" source="~/snippets/csharp/System/FlagsAttribute/Overview/flags.cs" interactive="try-dotnet" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/FlagsAttribute/Overview/flags.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.FlagsAttribute/VB/flags.vb" id="Snippet1":::
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]]></format>

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