Format text with placeholders

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Use Fmt.format when the same message pattern needs different values. Use string interpolation for a short message written directly in your code.

Import: import system.text;

import system;
import system.text;

fun main() {
    let args: object[] = ["Ada", 3];
    System.println(Fmt.format("Hello {0}, you have {1} items.", args));
}

Output: Hello Ada, you have 3 items.

Placeholder rules

{0} selects the first value in the argument array, {1} the second, and so on. Values are converted to text.

Pattern text	Output
{N}	Argument N (counting from zero) as text.
{N:.D}	A double or float argument rounded to exactly D decimal places.
{{	A literal {.
}}	A literal }.
{N} with a non-numeric or out-of-range N	The placeholder text unchanged, such as {5}.
{ with no closing }	A literal {.

.D is the only supported format specification. On a non-floating-point argument, or with any other specification after the colon, the value is written with its usual text representation.

The signature is Fmt.format(pattern: string, args: object[]): string. The pattern and values are separate, so you can reuse a message without rebuilding its wording.

See Fmt reference and Strings.