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ICustomFormatter F# snippets (dotnet#7765)
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‎snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs‎

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// <Snippet1>
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open System
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open System.Globalization
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open System.Numerics
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type BinaryFormatter() =
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interface IFormatProvider with
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// IFormatProvider.GetFormat implementation.
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member this.GetFormat(formatType: Type) =
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// Determine whether custom formatting object is requested.
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if formatType = typeof<ICustomFormatter> then
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this
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else
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null
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interface ICustomFormatter with
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// Format number in binary (B), octal (O), or hexadecimal (H).
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member this.Format(format, arg: obj, formatProvider: IFormatProvider) =
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// Handle null or empty format string, string with precision specifier.
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let thisFmt =
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// Extract first character of format string (precision specifiers
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// are not supported).
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if String.IsNullOrEmpty format |> not then
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if format.Length > 1 then
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format.Substring(0, 1)
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else
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format
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else
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String.Empty
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// Get a byte array representing the numeric value.
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let bytes =
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match arg with
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| :? sbyte as arg ->
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let byteString = arg.ToString "X2"
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Some [| Byte.Parse(byteString, NumberStyles.HexNumber) |]
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| :? byte as arg ->
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Some [| arg |]
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| :? int16 as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? int as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? int64 as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? uint16 as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? uint as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? uint64 as arg ->
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BitConverter.GetBytes arg
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|> Some
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| :? bigint as arg ->
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arg.ToByteArray()
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|> Some
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| _ ->
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None
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let baseNumber =
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match thisFmt.ToUpper() with
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// Binary formatting.
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| "B" -> Some 2
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| "O" -> Some 8
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| "H" -> Some 16
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// Handle unsupported format strings.
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| _ -> None
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match bytes, baseNumber with
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| Some bytes, Some baseNumber ->
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// Return a formatted string.
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let mutable numericString = String.Empty
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for i = bytes.GetUpperBound 0 to bytes.GetLowerBound 0 do
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let byteString = Convert.ToString(bytes[i], baseNumber)
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let byteString =
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match baseNumber with
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| 2 ->
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String('0', 8 - byteString.Length) + byteString
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| 8 ->
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String('0', 4 - byteString.Length) + byteString
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// Base is 16.
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| _ ->
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String('0', 2 - byteString.Length) + byteString
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numericString <- numericString + byteString + " "
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numericString.Trim()
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| _ ->
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try
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this.HandleOtherFormats(format, arg)
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with :? FormatException as e ->
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raise (FormatException($"The format of '{format}' is invalid.", e))
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member private this.HandleOtherFormats(format, arg: obj) =
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// <Snippet3>
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match arg with
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| :? IFormattable as arg ->
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arg.ToString(format, CultureInfo.CurrentCulture)
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| null ->
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String.Empty
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| _ ->
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string arg
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// </Snippet3>
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// </Snippet1>
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// <Snippet2>
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Console.WindowWidth <- 100
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let byteValue = 124uy
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// <Snippet4>
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String.Format(BinaryFormatter(), "{0} (binary: {0:B}) (hex: {0:H})", byteValue)
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|> printfn "%s"
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// </Snippet4>
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let intValue = 23045
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String.Format(BinaryFormatter(), "{0} (binary: {0:B}) (hex: {0:H})", intValue)
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|> printfn "%s"
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let ulngValue = 31906574882uL
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String.Format(BinaryFormatter(), "{0}\n (binary: {0:B})\n (hex: {0:H})", ulngValue)
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|> printfn "%s"
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let bigIntValue = BigInteger.Multiply(Int64.MaxValue, 2)
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String.Format(BinaryFormatter(), "{0}\n (binary: {0:B})\n (hex: {0:H})", bigIntValue)
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|> printfn "%s"
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// The example displays the following output:
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// 124 (binary: 01111100) (hex: 7c)
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// 23045 (binary: 00000000 00000000 01011010 00000101) (hex: 00 00 5a 05)
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// 31906574882
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// (binary: 00000000 00000000 00000000 00000111 01101101 11000111 10110010 00100010)
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// (hex: 00 00 00 07 6d c7 b2 22)
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// 18446744073709551614
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// (binary: 00000000 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111110)
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// (hex: 00 ff ff ff ff ff ff ff fe)
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// </Snippet2>

‎snippets/fsharp/System/ICustomFormatter/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="binaryformatter.fs" />
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</ItemGroup>
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</Project>

‎xml/System/ICustomFormatter.xml‎

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The following example implements <xref:System.ICustomFormatter> to allow binary, octal, and hexadecimal formatting of integral values. In this example, a single class, `IBinaryFormatter`, implements both <xref:System.ICustomFormatter> and <xref:System.IFormatProvider>. Its <xref:System.IFormatProvider.GetFormat%2A?displayProperty=nameWithType> method determines whether the `formatType` parameter represents an <xref:System.ICustomFormatter> type. If it does, `BinaryFormatter` returns an instance of itself; otherwise, it returns `null`. Its <xref:System.ICustomFormatter.Format%2A?displayProperty=nameWithType> implementation determines whether the format parameter is one of the three supported format strings ("B" for binary, "O" for octal, and "H" for hexadecimal) and formats the `arg` parameter appropriately. Otherwise, if `arg` is not `null`, it calls the `arg` parameter's <xref:System.IFormattable.ToString%2A?displayProperty=nameWithType> implementation, if one exists, or its parameterless `ToString` method, if one does not. If `arg` is `null`, the method returns <xref:System.String.Empty?displayProperty=nameWithType>.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet1":::
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`BinaryFormatter` can then be used to provide custom formatting by passing a `BinaryFormatter` object as the `provider` parameter of the <xref:System.String.Format%2A> method, as the following example shows.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet2":::
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]]></format>
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<xref:System.ICustomFormatter.Format%2A?displayProperty=nameWithType> is a callback method. It is called by a method that supports custom formatting, such as <xref:System.String.Format%28System.IFormatProvider%2CSystem.String%2CSystem.Object%5B%5D%29?displayProperty=nameWithType> or <xref:System.Text.StringBuilder.AppendFormat%28System.IFormatProvider%2CSystem.String%2CSystem.Object%5B%5D%29?displayProperty=nameWithType>. The implementation is called once for each format item in a [composite format string](/dotnet/standard/base-types/composite-formatting). For example, in the following statement, the <xref:System.ICustomFormatter.Format%2A?displayProperty=nameWithType> method is called three times.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet4":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet4":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet4":::
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The `arg` parameter is the object in the object list whose zero-based position corresponds to the index of a particular format item.
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Your implementation of the <xref:System.ICustomFormatter.Format%2A> method must include the following functionality so the .NET Framework can provide formatting you do not support. If your format method does not support a format, determine whether the object being formatted implements the <xref:System.IFormattable> interface. If it does, invoke the <xref:System.IFormattable.ToString%2A?displayProperty=nameWithType> method of that interface. Otherwise, invoke the default <xref:System.Object.ToString%2A?displayProperty=nameWithType> method of the underlying object. The following code illustrates this pattern.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet3":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet3":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet3":::
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The following example implements <xref:System.ICustomFormatter> to allow binary, octal, and hexadecimal formatting of integral values. Its <xref:System.ICustomFormatter.Format%2A?displayProperty=nameWithType> implementation determines whether the format parameter is one of the three supported format strings ("B" for binary, "O" for octal, and "H" for hexadecimal) and formats the `arg` parameter appropriately. Otherwise, if `arg` is not `null`, it calls the `arg` parameter's <xref:System.IFormattable.ToString%2A?displayProperty=nameWithType> implementation, if one exists, or its parameterless `ToString` method, if one does not. If `arg` is `null`, the method returns <xref:System.String.Empty?displayProperty=nameWithType>.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet1":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet1":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet1":::
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`BinaryFormatter` can then be used to provide custom formatting by passing a `BinaryFormatter` object as the `provider` parameter of the <xref:System.String.Format%2A> method, as the following example shows.
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:::code language="csharp" source="~/snippets/csharp/System/ICustomFormatter/Overview/binaryformatter.cs" id="Snippet2":::
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:::code language="fsharp" source="~/snippets/fsharp/System/ICustomFormatter/Overview/binaryformatter.fs" id="Snippet2":::
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:::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.icustomformatter.class/vb/binaryformatter.vb" id="Snippet2":::
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]]></format>

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