LEVIATHAN v962456e · 962456eee1

Standard Library

class Console

The program's standard output as an object.

since 0.1.0-alpha.1linuxwindows

Overview

Every program has one ready-made Console called console. write and writeln turn any value into its text form and print it, and << prints a string and returns the console so several writes chain. Output is text only; the console has no input side, and reading a line from standard input is done with sysReadLine.

Description

console is a global of class Console. It is an ordinary value: it is resolved and type-checked like any other, and you can store it in a variable or pass it around (Console c = console;).

  • console.write(value) writes any single value as text, with no newline.
  • console.writeln(value) writes the value followed by a newline.
  • console.writeln() writes just a newline.
  • console << text writes a string and returns the console, so writes chain: console << "a" << "b".

write and writeln accept a value of any type and convert it to text for you: strings print as they are, numbers print in decimal (a float prints six decimal places, 3.500000), a bool prints true or false, and an array prints as [1, 2, 3]. << takes a string.

A program's top-level statements run in order; there is no main function to define.

Writing to the console

console.write("no newline, ");
console.write(42);
console.writeln();
console.writeln("a string");
console.writeln(3.5);
console.writeln(true);
console.writeln([1, 2, 3]);
console << "chained " << "writes" << "\n";
Console alias = console;
alias.writeln("through an alias");
Run it ▶
no newline, 42
a string
3.500000
true
[1, 2, 3]
chained writes
through an alias

Rules

  • console is a const: console = Console(); is a compile error (cannot assign to const 'console').
  • write and writeln take one argument of any type; use string interpolation ("${a} and ${b}") to combine several values.
  • << takes a string, and returns the same console.
  • The output is standard output. A program that also writes to standard error should not rely on the relative order of the two, because standard output may be buffered.
  • Code that should not depend on the global console can take an IConsole parameter instead; see lang.capability-interfaces.

Examples

The program above shows each form. A function can also take the console as a value:

Passing the console around

void banner(Console out, string title) {
    out << "== " << title << " ==" << "\n";
    out.writeln("done");
}
banner(console, "report");
Run it ▶
== report ==
done

Notes

Console is not an OutStream; it has the same << shape without being one. A formal output interface for it is not part of the library yet.

Examples

console.write("total: ");
console.writeln(6 * 7);
console.writeln(true);
console << "chained " << "output\n";
Run it ▶
total: 42
true
chained output

Methods

write

write<T>(T v) -> void

Print the text form of a value without a trailing newline.

Strings print as they are, numbers and booleans as their usual text, and arrays and other objects in their printed form. Successive calls continue on the same line.

Parameters

v
The value to print.

Examples

console.write("a");
console.write(1);
console.write(true);
console.writeln();
console.writeln([1, 2, 3]);
Run it ▶
a1true
[1, 2, 3]

See also: writeln

writeln

writeln<T>(T v) -> void

Print the text form of a value followed by a newline.

A float prints with six decimals. Strings print as they are.

Parameters

v
The value to print.

Examples

console.writeln("hello");
console.writeln(42);
console.writeln(3.5);
console.writeln(false);
Run it ▶
hello
42
3.500000
false

writeln() -> void

Print a bare newline.

Use it to end a line that was built up with write, or to leave a blank line.

See also: write

Operators

<<

<<(string s) -> Console

Print a string and return the console, so several writes chain.

The argument must be a string; use toString() or an interpolated string to print another kind of value this way.

Parameters

s
The string to print.

Returns

This console.

Examples

int n = 3;
console << "n is " << n.toString() << "\n";
console << "done\n";
Run it ▶
n is 3
done

See also

  • console — The process console: the one Console every program can print to.
  • sysReadLine — Read one line of text from a file descriptor, without its trailing newline.
  • IConsole — What a program may say to the terminal.
  • OutStream — The writing end of a stream: you push values of type T in, and a reader takes them out.