FormattableString
has been Introduced in C# 6.0. As we can use same string formatting using string
object why is there need of using FormattableString
or IFormattable
. Whats difference between three?
My Code
var name = "Pravin"; var s = $"Hello, {name}"; System.IFormattable s1 = $"Hello, {name}"; System.FormattableString s2 = $"Hello, {name}";
Above all there produces same result. i.e 'Hello Pravin'.
Can I get more elaborated answer on this if anyone has deep knowledge on same.
In computer programming, string interpolation (or variable interpolation, variable substitution, or variable expansion) is the process of evaluating a string literal containing one or more placeholders, yielding a result in which the placeholders are replaced with their corresponding values.
IFormattable.ToString(String, IFormatProvider) Returns the string that results from formatting the format string along with its arguments by using the formatting conventions of a specified culture.
Syntax of string interpolation starts with a '$' symbol and expressions are defined within a bracket {} using the following syntax. Where: interpolatedExpression - The expression that produces a result to be formatted.
What is @ in front of a string in C#? It marks the string as a verbatim string literal. In C#, a verbatim string is created using a special symbol @. @ is known as a verbatim identifier.
FormattableString
is a new type in .NET 4.6, and the compiler will only use it if you try to use it. In other words, the type of an interpolated string literal is normally string
- built with string.Format
- but can be FormattableString
(via FormattableStringFactory
) if you ask for it.
A FormattableString
consists of the format string which would be passed to string.Format
(e.g. "Hello, {0}"
) and the arguments that would be passed in order to format it. Crucially, this information is captured before formatting.
This allows you to adjust the formatting appropriately - most commonly to perform it in the invariant culture, often with the Invariant
static method.
When you assign an interpolated string literal to an IFormattable
variable, that will use FormattableString
too. The IFormattable.ToString(string, CultureInfo)
implementation ignores the first argument in this case, which is presumably why it uses explicit interface implementation.
Sample code:
using System; using System.Globalization; using System.Threading; using static System.FormattableString; class Test { static void Main() { var uk = CultureInfo.CreateSpecificCulture("en-GB"); Thread.CurrentThread.CurrentCulture = uk; var germany = CultureInfo.CreateSpecificCulture("de-DE"); string now = $"Default: it is now {DateTime.UtcNow}"; Console.WriteLine(now); // UK format IFormattable x = $"Specific: It is now {DateTime.UtcNow}"; Console.WriteLine(x.ToString("ignored", germany)); FormattableString y = $"FormattableString: It is now {DateTime.UtcNow}"; Console.WriteLine(FormattableString.Invariant(y)); // Via using static Console.WriteLine(Invariant($"It is now {DateTime.UtcNow}")); } }
Sample results:
Default: it is now 16/02/2016 07:16:21 Specific: It is now 16.02.2016 07:16:21 FormattableString: It is now 02/16/2016 07:16:21 It is now 02/16/2016 07:16:21
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