F Sharp Strings

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String literals

let string1 = "Hello" //simple string

let string2 = "Line\nNewLine" //string with newline escape sequence

let string3 = @"Line\nSameLine" //use @ to create a verbatim string literal

let string4 = @"Line""with""quoutes inside" //double quoute to indicate a single quoute inside @ string

let string5 = """single "quote" is ok""" //triple-quote string literal, all symbol including quote are verbatim

let string6 = "ab
cd"// same as "ab\ncd"

let string7 = "xx\
    yy" //same as "xxyy", backslash at the end contunies the string without new line, leading whitespace on the next line is ignored

Simple string formatting

There are several ways to format and get a string as a result.

The .NET way is by using String.Format or StringBuilder.AppendFormat:

open System
open System.Text

let hello = String.Format ("Hello {0}", "World")
// return a string with "Hello World"

let builder = StringBuilder()
let helloAgain = builder.AppendFormat ("Hello {0} again!", "World")
// return a StringBuilder with "Hello World again!"

F# has also functions to format string in a C-style. There are equivalents for each .NET functions:

  • sprintf (String.Format) :
open System

let hello = sprintf "Hello %s" "World" 
// "Hello World", "%s" is for string

let helloInt = sprintf "Hello %i" 42 
// "Hello 42", "%i" is for int

let helloFloat = sprintf "Hello %f" 4.2 
// "Hello 4.2000", "%f" is for float

let helloBool = sprintf "Hello %b" true 
// "Hello true", "%b" is for bool

let helloNativeType = sprintf "Hello %A again!" ("World", DateTime.Now) 
// "Hello {formatted date}", "%A" is for native type

let helloObject = sprintf "Hello %O again!" DateTime.Now 
// "Hello {formatted date}", "%O" is for calling ToString
  • bprintf (StringBuilder.AppendFormat):
open System
open System.Text

let builder = StringBuilder()

// Attach the StringBuilder to the format function with partial application
let append format = Printf.bprintf builder format

// Same behavior as sprintf but strings are appended to a StringBuilder
append "Hello %s again!\n" "World"
append "Hello %i again!\n" 42
append "Hello %f again!\n" 4.2
append "Hello %b again!\n" true
append "Hello %A again!\n" ("World", DateTime.Now)
append "Hello %O again!\n" DateTime.Now

builder.ToString() // Get the result string

Using those functions instead of the .NET functions provides some advantages:

  • Type safety
  • Partial application
  • F# native type support

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