Module

std::io

I/O

Standard output, error printing, and structured I/O error types.

All types and functions live under the Io namespace.

Printing

Function	Stream	Newline	Accepts
`Io::print`	stdout	No	`String`
`Io::println`	stdout	Yes	`String`, `str`
`Io::eprint`	stderr	No	`String`
`Io::eprintln`	stderr	Yes	`String`, `str`

println and eprintln are overloaded for both String and str:

String overload: the value is consumed (moved), dropped after printing, and writes message.length() bytes.
str overload: writes the C string directly, no heap allocation.

print and eprint only accept String (no str overload). String overloads write message.length() bytes. str overloads remain NUL-terminated C-string writes and may stop at the first interior NUL. str overloads remain NUL-terminated C-string writes.

Error Types

Type	Source file	Description
`Io::ErrorKind`	error.ign	Category of the I/O error (8 variants)
`Io::IoError`	error.ign	Full error: kind + raw errno + strerror message

Example

import Io from "std::io";
import LibC from "std::libc";
import String from "std::string";

function main(): i32 {
  Io::println(String::create("hello, world!"));

  // I/O error from a failed syscall
  let fd: i32 = LibC::File::open("/nonexistent", LibC::File::O_RDONLY);
  if (fd == -1) {
    let err: Io::IoError = Io::IoError::lastError();
    // err.kind == Io::ErrorKind::NOT_FOUND
    // err.message == "No such file or directory"
    return 1;
  }

  return 0;
}

namespace Io

Standard I/O namespace.

println and eprintln have overloads for both String and str.

String overloads consume/move the value. str overloads forward the C string directly.

Functions

function eprint(message: String): void

Prints message to stderr without a trailing newline.

Arguments

message - The String to print (consumed/moved).

Example

import Io from "std::io";
import String from "std::string";

Io::eprint(String::create("warning: "));
Io::eprintln(String::create("low disk space"));

function eprintln(message: str): void

Prints a str message to stderr followed by a newline (\n).

Writes the C string directly via write(2), no heap allocation.

Arguments

message - The str literal or slice to print.

function eprintln(message: str): void

Prints a str message to stderr followed by a newline (\n).

Writes the C string directly via write(2), no heap allocation.

Arguments

message - The str literal or slice to print.

function print(message: String): void

Prints message to stdout without a trailing newline.

Useful for building up output incrementally or printing prompts.

Arguments

message - The String to print (consumed/moved).

Example

import Io from "std::io";
import String from "std::string";

Io::print(String::create("Enter name: "));

function println(message: str): void

Prints a str message to stdout followed by a newline (\n).

Writes the C string directly via write(2), no heap allocation.

Arguments

message - The str literal or slice to print.

function println(message: str): void

Prints a str message to stdout followed by a newline (\n).

Writes the C string directly via write(2), no heap allocation.

Arguments

message - The str literal or slice to print.

Functions

function __vectorStringMonomorphizationRoots(): void

Keeps Vector<String> monomorphizations reachable for std I/O builds.

Some std APIs return or manipulate Vector<String> only through code paths that may be optimized away in small programs. This internal root forces the compiler to instantiate clear/drop paths used by linked std modules.