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Format

format(fmt, ...args) renders a template string using {} placeholders, similar to Rust’s format! or Python’s str.format.

Basic placeholders

{} is replaced by the next argument, in order, using its default string representation.

format("Hello, {}!", "Alice")      // "Hello, Alice!"
format("{} + {} = {}", 1, 2, 3)    // "1 + 2 = 3"

Extra arguments beyond the number of placeholders are ignored.

Format specs — {:spec}

A placeholder may include a spec after a colon: {:[[fill]align][width][.precision][type]}.

Precision — floats

format("{:.2f}", 3.14159)   // "3.14"
format("{:.0f}", 9.7)       // "10"

Width and alignment

< left-aligns, > right-aligns, ^ centers. Numbers default to right-aligned; strings default to left-aligned.

format("{:>10}", "hi")   // "        hi"
format("{:<10}", "hi")   // "hi        "
format("{:^10}", "hi")   // "    hi    "

Fill character

A character placed immediately before the alignment symbol is used as padding instead of a space.

format("{:0>5d}", 42)    // "00042"
format("{:->8}", "x")    // "-------x"

Type specifiers

Type Meaning
f float, with optional .precision (default 6)
d integer, decimal
x integer, lowercase hex
o integer, octal
b integer, binary
s string (default) 
format("{:x}", 255)   // "ff"
format("{:o}", 8)     // "10"
format("{:b}", 5)     // "101"

If a value’s width exceeds the requested width, the value is not truncated.

Escaping braces

`` produce a literal { and }.

format("")   // "{not a placeholder}"

Errors

format() throws when:

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