formatstr

String interpolation library, complement of std/strformat for runtime pattern.

The main differences are that the arguments are to be called by format(), similarly to Python's str.format(), and that the pattern string can be set at runtime.

For example:

import formatstr

var str = "{} lives {:.1f} km from {:>10}."
echo str.format("Peio", 8 / 3, "Garazi.")

gives

Peio lives 2.7 km from     Garazi.

Numbered arguments

You can use numbers to indicate the argument to use (numbers start from 1):

let str = if character == "Yoda": "In {2}, {1} is" else: "{1} is in {2}"
echo str.format("Yoda", "Ryan", "the kitchen")

Warning : You cannot use unnumbered formats after the first numbered format

String arguments

By passing a table constructor with string literals as keys, arguments can be given by a string inside {}

echo "Hello {his name}, I am number {my number}".format({"my number": 33, "his name": "Bob"})

Keys must not contain ':' (characters after that become part of the specifier).

Warning : String arguments and other arguments are mutually exclusive

Format specifiers

The specification of standard format specifiers (after the :) is exactly the same as in strformat, as the library uses the same procedure formatValue.

Similarly to strformat, one can provide formatValue for a custom type:

import formatstr
type Person = object
  name: string
  age: int

proc formatValue(result: var string, arg: Person, spec: string) =
  result.add(arg.name)
  if 'a' in spec:
    result.add "(" & $arg.age & " years old)"

let person = Person(name: "Alice", age: 42)
check "{}".format(person) == "Alice"
check "{:a}".format(person) == "Alice(42 years old)"

should give

Alice
Alice(42 years old)

Installation

nimble install formatstr

Requirements

• Nim

License

MIT