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Range formatting documentation #3905

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30 changes: 27 additions & 3 deletions doc/syntax.rst
Original file line number Diff line number Diff line change
Expand Up @@ -491,13 +491,31 @@ Range Format Specifications
Format specifications for range types have the following syntax:

.. productionlist:: sf
range_format_spec: [":" [`underlying_spec`]]
range_format_spec: [":" ["n"][`range_type`][`range_underlying_spec`]]

The `underlying_spec` is parsed based on the formatter of the range's
The ``'n'`` option formats the range without the opening and closing brackets.

The available presentation types for `range_type` are:

+---------+----------------------------------------------------------+
| Type | Meaning |
+=========+==========================================================+
| ``'s'`` | String format. The range is formatted as a string. |
+---------+----------------------------------------------------------+
| ``'?s'``| Debug format. The range is formatted as an escaped |
| | string. |
+---------+----------------------------------------------------------+
| none | Default format. The range is formatted with a separator. |
+---------+----------------------------------------------------------+

If `range_type` is ``'s'`` or ``'?s'``, the range element type must be a character type. The
``'n'`` option and `range_underlying_spec` are mutually exclusive with ``'s'`` and ``'?s'``.

The `range_underlying_spec` is parsed based on the formatter of the range's
reference type.

By default, a range of characters or strings is printed escaped and quoted. But
if any `underlying_spec` is provided (even if it is empty), then the characters
if any `range_underlying_spec` is provided (even if it is empty), then the characters
or strings are printed according to the provided specification.

Examples::
Expand All @@ -508,6 +526,12 @@ Examples::
// Result: [0xa, 0x14, 0x1e]
fmt::format("{}", vector{'h', 'e', 'l', 'l', 'o'});
// Result: ['h', 'e', 'l', 'l', 'o']
fmt::format("{:n}", vector{'h', 'e', 'l', 'l', 'o'});
// Result: 'h', 'e', 'l', 'l', 'o'
fmt::format("{:s}", vector{'h', 'e', 'l', 'l', 'o'});
// Result: "hello"
fmt::format("{:?s}", vector{'h', 'e', 'l', 'l', 'o', '\n'});
// Result: "hello\n"
fmt::format("{::}", vector{'h', 'e', 'l', 'l', 'o'});
// Result: [h, e, l, l, o]
fmt::format("{::d}", vector{'h', 'e', 'l', 'l', 'o'});
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