format

Description:

format

format #
It is a package for formatting Dart strings. It contains: the format
function and the extension methods of the String class: format and print.
Function format similar to format
method in Python, std::format
function from C++20, which in turn became the development of the popular
function sprintf from C. Its
essence is that instead of templates enclosed in curly braces {}, substitute
the values of the passed arguments, formatting them as required.
String result = '{...}'.format(...);
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Usage example #
Hello world:
format('{}', 'hello world'); // hello world
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Values as function arguments (max 10 values):
format('{} {}', 'hello', 'world'); // hello world
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Values as positional arguments (unlimited number of values):
format('{} {}', ['hello', 'world']);
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Manual numbering of positional arguments:
format('{0} {1}', 'hello', 'world'); // hello world
format('{1} {0}', 'hello', 'world'); // world hello
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Values as named arguments:
format('{h} {w}', {'h': 'hello', 'w': 'world'}); // hello world
format('{w} {h}', {#h: 'hello', #w: 'world'}); // world hello
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Number formatting:
print('| Name | Price | Count | Sum |');
print(
'| {name:8s} | {price:8.2f} | {count:8d} | {sum:8.2f} |'.format({
#name: 'Apple',
#price: 1.2,
#count: 9,
#sum: 10.8,
}),
);

// | Name | Price | Count | Sum |
// | Apple | 1.20 | 9 | 10.80 |
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Unicode:
format('{:🇺🇦^12}', ' No war '); // 🇺🇦🇺🇦 No war 🇺🇦🇺🇦
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Locale:
Intl.defaultLocale = 'uk_UA';
format('{:,.8n}', 123456.789); // 123 456,79

Intl.defaultLocale = 'bn';
format('{:,.8n}', 123456.789); // ১,২৩,৪৫৬.৭৯
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Differences from Python #


Python supports only one type of argument numbering at a time: either
automatic numbering ({} {} {}) or manual numbering ({0} {1} {2}).
I've added the ability to use both types of numbering at the same time:
format('{0} {}->1 {}->2 {5} {}->6'); // 0 1 2 5 6
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Named parameters can be specified in national languages according to the same
principle as Latin characters: the identifier must start with a letter or an
underscore and then digits can be added (Unicode is used). Parameter names
can be specified in quotes (both single and double). There are no
restrictions in this case. Quotation marks inside names must be double-quoted
to avoid being perceived as the end of the identifier.
format('{가격}', {'가격': 123.45});
format("{'It''s a name'}", {"It's a name": 'Name'});
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The alternative format for X outputs 0x instead of 0X (0xABCDEF
instead of 0XABCDEF).
format('{0:#x} {0:#X}', 0xabcdef); // 0xabcdef 0xABCDEF
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I did not support an alternative format for b (0b...) and o (0o...),
since Dart does not support such literals. Let me know if you need it.


nan and inf are not complemented with zeros when the zero flag is set
(as Python does, but msvc:spintf does not). sign does not work for nan
(nan cannot become +nan) (Python and msvc:sprintf output +nan).
In short, neither nan nor inf changes in any way. Only the width
alignment works. And this is done deliberately. Nobody, as I think, needs
+nan, 000nan and 000inf.


In g and n formats, the default precision is 6.


To support surrogate pairs and other combinations of Unicode characters,
fill can accept any number of characters, as long as it ends with one of
the align characters (>, <, ^).


Not supported in named arguments .key and index. That's an interesting
solution. I like it. But I didn't.


In exponential notation (e and g) in Python, the exponent is returned
with at least two digits. I have one.


In n format, E5 is output instead of e+05. This is how NumberFormat
works by default.


Does not support = in align.


Doesn't support %.


{} only supports width and precision, while Python supports {}
anywhere to form a pattern. But this can easily be replaced with ${}.