String Formatting in Nim

import strformat

type
  Point = object
    x, y: int

proc main() =
  # Nim offers excellent support for string formatting.
  # Here are some examples of common string formatting tasks.

  # Nim uses string interpolation with the `&` operator
  # and format specifiers similar to printf traditions.

  let p = Point(x: 1, y: 2)
  echo &"struct1: {p}"

  # To include field names, we can use the `$` operator
  echo &"struct2: {$p}"

  # Nim doesn't have a direct equivalent to Go's %#v,
  # but we can create a custom representation
  echo &"struct3: Point(x: {p.x}, y: {p.y})"

  # To print the type of a value, use `type()`
  echo &"type: {type(p)}"

  # Formatting booleans is straightforward
  echo &"bool: {true}"

  # There are many options for formatting integers
  echo &"int: {123}"

  # This prints a binary representation
  echo &"bin: {14:b}"

  # This prints the character corresponding to the given integer
  echo &"char: {char(33)}"

  # Hex encoding
  echo &"hex: {456:x}"

  # Formatting floats
  echo &"float1: {78.9:.6f}"

  # Scientific notation
  echo &"float2: {1.234e8:.6e}"
  echo &"float3: {1.234e8:.6E}"

  # String formatting
  echo &"str1: \"string\""

  # To double-quote strings, use the `escape` proc
  import strutils
  echo &"str2: {escape("""string""")}"

  # Hex representation of a string
  echo &"str3: {toHex("hex this")}"

  # To print a representation of a pointer
  echo &"pointer: {cast[int](addr p):x}"

  # Controlling width and precision
  echo &"width1: |{12:6}|{345:6}|"
  echo &"width2: |{1.2:6.2f}|{3.45:6.2f}|"
  echo &"width3: |{1.2:<6.2f}|{3.45:<6.2f}|"

  # Formatting strings with width
  echo &"width4: |{"foo":>6}|{"b":>6}|"
  echo &"width5: |{"foo":<6}|{"b":<6}|"

  # Nim's equivalent of Sprintf is the `&` operator
  let s = &"sprintf: a {"string"}"
  echo s

  # To write to stderr, use the `stderr` file descriptor
  stderr.writeLine &"io: an {"error"}"

main()

To run the program, save it as string_formatting.nim and use the Nim compiler:

$ nim c -r string_formatting.nim

This will compile and run the program, producing output similar to the original Go example.

Nim’s string formatting capabilities are quite powerful, using string interpolation with the & operator and format specifiers similar to those in other languages. The strformat module provides this functionality.

Note that Nim doesn’t have exact equivalents for all of Go’s formatting verbs, but it offers similar capabilities through its own syntax and standard library functions.

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String Formatting in Nim