2017 © Pedro Peláez

library format

Library for string formatting.



Library for string formatting.

  • Saturday, March 18, 2017
  • by Fleshgrinder
  • Repository
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  • 2 Stars
  • 2,961 Installations
  • PHP
  • 2 Dependents
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  • 3 Versions
  • 42 % Grown


Latest Stable Version License Travis CI build status AppVeyor CI build status, (*1)

Dependency Status Coveralls branch Scrutinizer Code Climate: GPA Total Downloads, (*2)


The format library provides the functionality to format special string patterns. The implementation is similar to sprintf and msgfmt_format_message but with various unique and very useful features., (*3)


Open a terminal, enter your project directory and execute the following command to add this library to your dependencies:, (*4)

composer require fleshgrinder/format

This command requires you to have Composer installed globally, as explained in the installation chapter of the Composer documentation., (*5)


This library features a single static method to format string patterns. Some examples of the format method are:, (*6)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('Hello, {}!', ['World'])    === 'Hello, World!');
assert(Formatter::format('The number is {}', [1000]) === 'The number is 1,000');
assert(Formatter::format('{}', [[1, 2, 3]])          === '1, 2, 3');
assert(Formatter::format('{value}', ['value' => 42]) === '42');
assert(Formatter::format('{} {}', [1, 2])            === '1 2');
assert(Formatter::format('{.3}', [0.123456789])      === '0.123');
assert(Formatter::format('{.2:and}', [[1, 2, 3]])    === '1.00, 2.00, and 3.00');
assert(Formatter::format('{#b}', [2])                === '0b10');
assert(Formatter::format('{:?}', [tmpfile()])        === 'stream resource');


Each placeholder can specify which argument value it references, and if omitted it is assumed to be “the next argument”. For example, the pattern {} {} {} would take three arguments, and they would be formatted in the same order as they are given. The pattern {2} {1} {0}, however, would format arguments in reverse order., (*7)

Things can get a little tricky once you start intermingling the two types of positional placeholders. The “next argument” specifier can be thought of as an iterator over the arguments. Each time a “next argument” specifier is seen, the iterator advances. This leads to behavior like this:, (*8)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{1} {} {0} {}', [1, 2]) === '2 1 1 2');

The internal iterator over the arguments has not been advanced by the time the first {} is seen, so it prints the first argument. Then upon reaching the second {}, the iterator has advanced forward to the second argument. Essentially, placeholders which explicitly specify their argument do not affect placeholders which do not specify an argument in terms of positional placeholders., (*9)

Placeholders are not limited to numbers, it is also possible to access them by names. Names are limited to A-Za-z0-9_- characters, this ensures highest compatibility and should match 99 % of all associative array keys in the PHP world:, (*10)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{placeholder}', ['placeholder' => 'test'])        === 'test');
assert(Formatter::format('{placeholder} {}', ['placeholder' => 2, 1])       === '2 1');
assert(Formatter::format('{a} {c} {b}', ['a' => 'a', 'b' => 'b', 'c' => 3]) === 'a 3 b');

A pattern is required to use all placeholders, but not all arguments. A MissingPlaceholderException is thrown if a placeholder is missing from the arguments:, (*11)

<?php use Fleshgrinder\Core\Formatter;
use Fleshgrinder\Core\Formatter\MissingPlaceholderException;

try {
    Formatter::format('{}', []);
catch (MissingPlaceholderException $e) {
    assert($e->getMessage() === 'Placeholder `0` missing from arguments, got empty array');

You may refer to the same argument more than once in the pattern, including different modifiers (which are explained in the following sections)., (*12)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{a} {a} {a}', ['a' => 'foo']) === 'foo foo foo');

Type Modifier

The type modifier can be used to print the type of an argument value instead of attempting to format the value itself:, (*13)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{:?}', [])             === 'void');
assert(Formatter::format('{:?}', [[]])           === 'array');
assert(Formatter::format('{:?}', [true])         === 'boolean');
assert(Formatter::format('{:?}', [false])        === 'boolean');
assert(Formatter::format('{:?}', [1.2])          === 'float');
assert(Formatter::format('{:?}', [1])            === 'integer');
assert(Formatter::format('{:?}', [null])         === 'null');
assert(Formatter::format('{:?}', [new stdClass]) === 'stdClass');
assert(Formatter::format('{:?}', [new DateTime]) === 'DateTime');
assert(Formatter::format('{:?}', [tmpfile()])    === 'stream resource');
assert(Formatter::format('{:?}', [''])           === 'string');

Combination with positional and named placeholders is of course possible:, (*14)

<?php use Fleshgrinder\Core\{Formatter, Value};

        'Expected argument of type {expected}, got {actual:?}',
        ['expected' => Value::TYPE_ARRAY, 'actual' => '']
    ) === 'Expected argument of type array, got string'

The fleshgrinder/value library is used to get the type of the value, this means in effect that type names are consistent in naming and case. However, the output for resources is slightly extended by including the type of the resource:, (*15)

<?php use Fleshgrinder\Core\{Formatter, Value};

$r = tmpfile();

assert(Value::getType($r)              === 'resource');
assert(Formatter::format('{:?}', [$r]) === 'stream resource');


The type modifier cannot be combined with any other modifier and always overwrites anything else!, (*17)

String Formatting and Modifiers

The method is binary safe and strings are printed as is., (*18)

Since version 1.1.0 empty strings and objects that can be converted to strings are formatted as empty {:?} instead of resulting in no output at all:, (*19)

<?php namespace Fleshgrinder\Examples;

use Fleshgrinder\Core\Formatter;

class Stringable { function __toString() { return ''; } }

assert(Formatter::format('{}', ['']) === 'empty string');
assert(Formatter::format('{}', [new Stringable]) === 'empty Fleshgrinder\Examples\Stringable');

Also available since 1.1.0 are the caret notation modifier c and the printable Unicode replacement modifier p for ASCII control characters:, (*20)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{#c}', ["\0\n"]) === '^@^J');
assert(Formatter::format('{#p}', ["\0\n"]) === '␀␊');

This is useful while constructing error messages where a string that violated some constraint should be included in the error message, but might lead to undesired side-effects due to the nature of control characters. Both string modifiers help to mitigate this problem. Note that recreation of the original string might be impossible with the caret notation, the printable Unicode replacements should be used in such cases. However, those characters are UTF-8 characters and not ASCII characters, which might not be acceptable., (*21)

Number Formatting and Modifiers

Numbers are formatted with number_format and its default values for decimal and thousand separators, this ensures best readability and consistent formatting. The amount of decimals defaults to zero, but may be configured by inserting a natural number separated by a dot (.) within the braces after the placeholder:, (*22)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{.3}', [1.23456])   === '1.235');
assert(Formatter::format('$ {.2}', [9999.99]) === '$ 9,999.99');
assert(Formatter::format('{0.3}', [1.2345])   === '1.235');
assert(Formatter::format('{a.2}', ['a' => 1]) === '1.00');

The output format of numbers can be changed with format modifiers. A format modifier is added by inserting the desired modifier after a hash symbol (#) within the braces after the placeholder. Available format modifiers are:, (*23)

  • #b for binary numbers,
  • #e for exponent notation,
  • #o for octal, and
  • #x for hexadecimal.
<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{#b}', [2])           === '0b10');
assert(Formatter::format('{#e}', [0.123456789]) === '1.234568e-1');
assert(Formatter::format('{#o}', [493])         === '0o755');
assert(Formatter::format('{#x}', [42])          === '0x2A');

Note that there are no #E or #X modifiers, this is on purpose to force consistent output., (*24)

Iterable Listings and Modifiers

Iterable data structures are formatted as comma-separated lists. An optional conjunction may be configured by adding the desired word after a colon (:) inside the braces after the placeholder:, (*25)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{}', [[]])                 === 'empty array');
assert(Formatter::format('{}', [new ArrayIterator])  === 'empty ArrayIterator');
assert(Formatter::format('{}', [['a']])              === 'a');
assert(Formatter::format('{}', [['a', 'b']])         === 'a, b');
assert(Formatter::format('{}', [['a', 'b', 'c']])    === 'a, b, c');
assert(Formatter::format('{:and}', [['a', 'b']])     === 'a and b');
assert(Formatter::format('{:or}', [['a', 'b', 'c']]) === 'a, b, or c');

This is perfect for the construction of error messages:, (*26)

<?php use Fleshgrinder\Core\Formatter;

try {
    $expected = ['a', 'b', 'c'];
    $actual   = 'x';

    if (in_array($actual, $expected, true) === false) {
        throw new InvalidArgumentException(Formatter::format(
            'Value must be one of {expected:or}, got {actual}',
            ['expected' => $expected, 'actual' => $actual]
catch (InvalidArgumentException $e) {
    assert($e->getMessage() === 'Value must be one of a, b, or c, got x');

Other modifiers, except for type, are of course combinable with iterable listings:, (*27)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{.1:and}', [[0, 1, 2]])   === '0.0, 1.0, and 2.0');
assert(Formatter::format('{#b:and}', [[0, 1, 2]])   === '0b0, 0b1, and 0b10');
assert(Formatter::format('{#o:and}', [[7, 8, 9]])   === '0o7, 0o10, and 0o11');
assert(Formatter::format('{#x:and}', [[9, 10, 11]]) === '0x9, 0xA, and 0xB');

Note well that expansion of iterable data structures is recursive, this might lead to unexpected output, but it might also result in infinite loops in case the data structure contains circular references. Ensure that your iterable argument values are sane, you have been warned:, (*28)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('{}', [[0, [1, 2], 3]]) === '0, 1, 2, 3');

Optional Parts

Another unique feature are optional parts, which are included only if a marked argument is present and contains a non-empty value (according to PHP’s empty rules). Optional parts are specified by enclosing some text in brackets:, (*29)

<?php use Fleshgrinder\Core\Formatter;

$pattern = 'This is always printed[, and this is printed only if {this_argument}? is non-empty]';

    Formatter::format($pattern, ['this_argument' => ''])
    === 'This is always printed'

    Formatter::format($pattern, ['this_argument' => 'this argument'])
    === 'This is always printed, and this is printed only if this argument is non-empty'

A placeholder is marked by appending a question mark (?) after the closing brace of the placeholder. All marked placeholders within an optional part must be non-empty in order to be included. Note that no exception is thrown if a marked placeholder within an optional part is missing from the arguments, as this counts as being empty. Note further that nesting of optional parts is not possible, however, if you think that this would be greater feature feel free to open an issue., (*30)


Only fixed positional and named placeholders can be marked, the internal argument iterator is not taken into account. This means in effect that a pattern like the following never includes the optional part because there is no fixed positional or named placeholder present:, (*32)

<?php use Fleshgrinder\Core\Formatter;
  assert(Formatter::format('[{}?]', ['foobar']) === '');

The reason for this limitation is simple: optional parts are evaluated separately before the full pattern is being evaluated. Hence, any internal iterator would start counting inside the optional part, which would lead to hard to understand and weird behavior; if supported., (*33)


The special characters [, ], {, and } can be escaped by doubling them, [[, ]], {{, or }} respectively., (*34)

<?php use Fleshgrinder\Core\Formatter;

assert(Formatter::format('[[{.1}, {.1}]]', [0, 1])     === '[0.0, 1.0]');
assert(Formatter::format('{:con}}junction}', [[0, 1]]) === '0 con}junction 1');

Errors and Exceptions

Any error or exception that might be thrown by an argument that is being formatted is not caught and bubbles up. The method itself throws the already explained MissingPlaceholderException. It might throw an InvalidArgumentException as well, if the type modifier is not present and an argument is:, (*35)

  • a resource—as there is no meaningful way to format them—or
  • an object that is not Traversable, and has none of the following methods:
    • __toString
    • toFloat
    • toInt
    • toString


Open a terminal, enter the project directory and execute the following commands to run the PHPUnit tests with your locally installed PHP executable. This requires that you have at least make 4.0 installed:, (*36)


You can also execute the following two commands, in case make is not available on your system, or too old:, (*37)

composer install
composer test

The Versions

18/03 2017



Library for string formatting.

  Sources   Download


The Requires


The Development Requires

formatting error-messages

16/03 2017


Library for string formatting.

  Sources   Download


The Requires


The Development Requires

formatting error-messages

12/03 2017


Library for string formatting.

  Sources   Download


The Requires


The Development Requires

formatting error-messages