formatterpythonstyle.inl

Go to the documentation of this file.

//==================================================================================================
/// \file
/// This header-file is part of module \alib_format of the \aliblong.
///
/// \emoji :copyright: 2013-2025 A-Worx GmbH, Germany.
/// Published under \ref mainpage_license "Boost Software License".
//==================================================================================================
ALIB_EXPORT namespace alib::format {
 
//==================================================================================================
/// Implements a \alib{format;Formatter} according to the
/// \https{formatting standards of the Python language,docs.python.org/3.5/library/string.html#format-string-syntax}.
///
/// \note
///   Inherited, public fields of parent class \b FormatterStdImpl provide important possibilities
///   for changing the formatting behavior of instances of this class. Therefore, do not forget
///   to consult the \ref alib::format::FormatterStdImpl "parent classes documentation".
///
/// In general, the original \b Python specification is covered quite well. However, there are
/// some differences, some things are not possible (considering python being a scripting language)
/// but then there are also found some very helpful extensions to that standard. Instead of repeating
/// a complete documentation, please refer to the
/// \https{Python Documentation,docs.python.org/3.5/library/string.html#format-string-syntax}
/// as the foundation and then take note of the following list of differences, extensions and
/// general hints:
///
/// - <b>General Notes:</b>
///   \b Python defines a placeholder field as follows
///
///          "{" [field_name] ["!" conversion] [":" format_spec] "}"
///
///
///   - This formatter is <b>less strict</b> in respect to the order of the format symbols. E.g.
///     it allows <c>{:11.5,}</c> where Python allows only <c>{:11,.5}</c>
///
///   - With this class being derived from
///     \ref alib::format::FormatterStdImpl "FormatterStdImpl", features of the parent are
///     available to this formatter as well. This is especially true and sometimes useful in respect to
///     setting default values number formatting. For example, this allows modifying all number output
///     without explicitly repeating the settings in each placeholder of format strings. Other options,
///     for example, the grouping characters used with hexadecimal numbers, cannot be even changed
///     with the <b>Python Style</b> formatting options. The only way of doing so is modifying the
///     properties of the formatter object before the format operation.
///
///   - Nested replacements in format specification fields are (by nature of this implementation
///     language) \b not supported.
///
/// <p>
/// - <b>Positional arguments and field name:</b>
///   - By the nature of the implementation language (<em>C++, no introspection</em>) of this class,
///     \b field_name can \b not be the name of an identifier, an attribute name or an array element
///     index. It can only be a positional argument index, hence a number that chooses a different
///     index in the provided argument list.<br>
///     However, the use of field names is often a requirement in use cases that offer configurable
///     format string setup to the "end user". Therefore, there are two alternatives to cope
///     with the limitation:
///     - In simple cases, it is possible to just add all optionally needed data in the argument list,
///       document their index position and let the user use positional argument notation to choose
///       the right value from the list.
///     - More elegant however, is the use of class
///       \ref alib::format::PropertyFormatter "PropertyFormatter"
///       which extends the format specification by custom identifiers which control the placement
///       of corresponding data in the format argument list. This class uses a translator table from
///       identifier strings to custom callback functions. This way, much more than just simple
///       field names are allowed.
///
///   - When using positional arguments in a format string placeholders, the Python formatter
///     implementation does not allow to switch from <b>automatic field indexing</b> to explicit
///     indexing. This \b %Aib implementation does allow it. The automatic index (aka no positional
///     argument is given for a next placeholder) always starts with index \c 0 and is incremented
///     each time automatic indexing is used.   Occurrences of explict indexing have no influence
///     on the automatic indexing.
///
///
/// <p>
/// - <b>Binary, Hexadecimal and Octal Numbers:</b>
///   - Binary, hexadecimal and octal output is <b>cut in size</b> (!) when a field width is given that
///     is smaller than the resulting amount of digits of the number arguments provided.
///      \note  This implies that a value written might not be equal to the value given.
///             This is not a bug but a design decision. The rationale behind this is that with this
///             behavior, there is no need to mask lower digits when passing the arguments to the
///             format invocation. In other words, the formatter "assumes" that the given field width
///             indicates that only a corresponding number of lower digits are of interest.
///
///   - If no width is given and the argument contains a boxed pointer, then the platform-dependent
///     full output width of pointer types is used.
///
///   - The number <b>grouping option</b> (<c>','</c>) can also be used with binary, hexadecimal and octal
///     output.
///     The types support different grouping separators for nibbles, bytes, 16-bit and 32-bit words.
///     Changing the separator symbols, is not possible with the format fields of the format strings
///     (if it was, this would become very incompatible to Python standards). Changes have to be made
///     before the format operation by modifying field
///     \alib{format;FormatterStdImpl::AlternativeNumberFormat;FormatterStdImpl::AlternativeNumberFormat}
///     which is provided through parent class \b %FormatterStdImpl.
///
///   - Alternative form (\c '#') adds prefixes as specified in members
///     - \alib{strings;TNumberFormat::BinLiteralPrefix;BinLiteralPrefix},
///     - \alib{strings;TNumberFormat::HexLiteralPrefix;HexLiteralPrefix}, and
///     - \alib{strings;TNumberFormat::OctLiteralPrefix;OctLiteralPrefix}.
///
///     For upper case formats,  those are taken from field
///     \alib{format;FormatterStdImpl::DefaultNumberFormat;FormatterStdImpl::DefaultNumberFormat},
///     for lower case formats from
///     \alib{format;FormatterStdImpl::AlternativeNumberFormat;FormatterStdImpl::AlternativeNumberFormat}.
///     However, in alignment with the \b Python specification, \b both default to lower case
///     literals \c "0b", \c "0o" and \c "0x". All defaults may be changed by the user.
///
///
/// <p>
/// - <b>Floating point values:</b>
///   - If floating point values are provided without a type specification in the format string, then
///     all values of
///     \alib{format;FormatterStdImpl::DefaultNumberFormat;FormatterStdImpl::DefaultNumberFormat}
///     are used to format the number
///   - For lower case floating point format types (\c 'f' and \c 'e'), the values specified in
///     attributes \b %ExponentSeparator, \b %NANLiteral and \b %INFLiteral of object
///     \alib{format;FormatterStdImpl::AlternativeNumberFormat;FormatterStdImpl::AlternativeNumberFormat}
///     are used. For upper case   types (\c 'F' and \c 'E') the corresponding attributes in
///     \alib{format;FormatterStdImpl::DefaultNumberFormat;FormatterStdImpl::DefaultNumberFormat} apply.
///   - Fixed point formats (\c 'f' and 'F' types) are not supported to use an arbitrary length.
///     See class \alib{strings;TNumberFormat;NumberFormat} for the limits.
///     Also, very high values and values close to zero may be converted to scientific format.
///     Finally, if flag \alib{strings;NumberFormatFlags;ForceScientific} field
///     \alib{strings::NumberFormat;Flags} in member #DefaultNumberFormat is \c true, types
///     \c 'f' and 'F' behave like types \c 'e' and 'E'.
///   - When both, a \p{width} and a \p{precision} is given, then the \p{precision} determines the
///     fractional part, even if the type is \b 'g' or \b 'G'. This is different than specified with
///     Python formatter, which uses \p{precision} as the overall width in case of types
///     \b 'g' or \b 'G'.
///   - The 'general format' type for floats, specified with \c 'g' or \c 'G' in the python
///     implementation limits the precision of the fractional part, even if \p{precision} is not
///     further specified. This implementation does limit the precision only if type is \c 'f'
///     or \c 'F'.
///
/// <p>
/// - <b>%String Conversion:</b><br>
///   If \e type \c 's' (or no \e type) is given in the \b format_spec of the replacement field,
///   a string representation of the given argument is used.
///   In \b Java and \b C# such representation is received by invoking <c>Object.[t|T]oString()</c>.
///   Consequently, to support string representations of custom types, in these languages
///   the corresponding <b>[t|T]oString()</b> methods of the type have to be implemented.
///
///   In C++ the arguments are "boxed" into objects of type
///   \ref alib::boxing::Box "Box". For the string representation, the formatter invokes
///   box-function \alib{boxing;FAppend}. A default implementation exists which
///   for custom types appends the type name and the memory address of the object in hexadecimal
///   format. To support custom string representations (for custom types), this box-function
///   needs to be implemented for the type in question. Information and sample code on how to do this
///   is found in the documentation of \alib_boxing , chapter
///   \ref alib_boxing_strings_fappend "10.3 Box-Function FAppend".
///
/// - <b>Hash-Value Output:</b><br>
///   In extension (and deviation) of the Python specification, format specification type \c 'h' and
///   its upper case version \c 'H' is implemented. The hash-values of the argument object is
///   written in hexadecimal format. Options of the type are identical to those of \c 'x',
///   respectively \c 'X'.
///
///   In the C++ language implementation of \alib, instead of hash-values of objects, the pointer
///   found in method \alib{boxing;Box::Data} is printed. In case of boxed class-types and default
///   boxing mechanics are used with such class types, this will show the memory address of
///   the given instance.
///
/// - <b>Boolean output:</b><br>
///   In extension (and deviation) of the Python specification, format specification type \c 'B'
///   is implemented. The word \b "true" is written if the given value represents a boolean \c true
///   value, \b "false" otherwise.
///
///   In the C++ language implementation of \alib, the argument is evaluated to boolean by invoking
///   box-function \alib{boxing;FIsTrue}.
///
/// <p>
/// - <b>%Custom %Format Specifications:</b><br>
///   With \c Python formatting syntax, placeholders have the following syntax:
///
///          "{" [field_name] ["!" conversion] [":" format_spec] "}"
///
///   The part that follows the colon is called \b format_spec. \b Python passes this portion of the
///   placeholder to a built-in function \c format(). Now, each type may interpret this string in a
///   type specific way. But most built-in \b Python types do it along what they call the
///   \https{"Format Specification Mini Language",docs.python.org/3.5/library/string.html#format-specification-mini-language}.
///
///   With this implementation, the approach is very similar. The only difference is that the
///   "Format Specification Mini Language" is implemented for standard types right within this class.
///   But before processing \b format_spec, this class will check if the argument type assigned to
///   the placeholder disposes of a custom implementation of box function \alib{format;FFormat}.
///   If so, this function is invoked and string \b format_spec is passed for custom processing.
///
///   Information and sample code on how to adopt custom types to support this interface is
///   found in the Programmer's Manual of this module, with chapter
///   \ref alib_format_custom_types_fformat.
///
///   For example, \alib class \alib{time;DateTime} supports custom formatting with box-function
///   \alib{format;FFormat_DateTime} which uses helper-class
///   \alib{strings::util;CalendarDateTime} that provides a very common specific mini language
///   for \alib{strings::util::CalendarDateTime;Format;formatting date and time values}.
///
/// <p>
/// - <b>Conversions:</b><br>
///   In the \b Python placeholder syntax specification:
///
///          "{" [field_name] ["!" conversion] [":" format_spec] "}"
///
///   symbol \c '!' if used before the colon <c>':'</c> defines
///   what is called the <b>conversion</b>. With \b Python, three options are given:
///   \c '!s' which calls \c str() on the value, \c '!r' which calls \c repr() and \c '!a' which
///   calls \c ascii(). This is of course not applicable to this formatter. As a replacement,
///   this class extends the original specification of that conversion using \c '!'.
///   The following provides a list of conversions supported. The names given can be abbreviated
///   at any point and ignore letter case, e.g., \c !Upper can be \c !UP or just \c !u.
///   In addition, multiple conversions can be given by concatenating them, each repeating
///   character \c '!'.<br>
///   The conversions supported are:
///
///   - <b>!Upper</b><br>
///     Converts the contents of the field to upper case.
///
///   - <b>!Lower</b><br>
///     Converts the contents of the field to lower case.
///
///   - <b>!Quote[O[C]]</b><br>
///     Puts quote characters around the field.
///     Note that these characters are not respecting any optional given field width but instead
///     are added to such.
///     An alias name for \!Quote is given with \b !Str. As the alias can be abbreviated to \b !s,
///     this provides compatibility with the \b Python specification.
///
///     In extension to the python syntax specification, one or two optional characters might be
///     given after the (optionally abreviated) terms "Quote" respectively "str".
///     If one character is given, this is used as the open and closing character. If two are given,
///     the first is used as the open character, the second as the closing one.
///     For example, <b>{!Q'}</b> uses single quotes, or <b>{!Q[]}</b> uses rectangular brackets.
///     Bracket types <b>'{'</b> and <b>'}'</b> cannot be used with this conversion.
///     To surround a placeholder's contents in this bracket type, add <b>{{</b> and <b>}}</b>
///     around the placeholder - resulting in <b>{{{}}}</b>!.
///
///   - <b>!ESC[<|>]</b><br>
///     In its default behavior or if \c '<' is specified, certain characters are converted to escape
///     sequences.
///     If \c '>' is given, escape sequences are converted to their (ascii) value.
///     See \alib{strings;TEscape;Escape} for details about the conversion
///     that is performed.<br>
///     An alias name for \b !ESC< is given with \b !a which provides compatibility
///     with the \b Python specification.
///     \note If \b !ESC< is used in combination with \b !Quote, then \b !ESC< should be the first
///           conversion specifier. Otherwise, the quotes inserted might be escaped as well.
///
///   - <b>!Fill[Cc]</b><br>
///     Inserts as many characters as denoted by the integer type argument.
///     By default the fill character is space <c>' '</c>. It can be changed with optional character
///     'C' plus the character wanted.
///
///   - <b>!Tab[Cc][NNN]</b><br>
///     Inserts fill characters to extend the length of the string to be a multiple of a tab width.
///     By default the fill character is space <c>' '</c>. It can be changed with optional character
///     'C' plus the character wanted. The tab width defaults to \c 8. It can be changed by adding
///     an unsigned decimal number.
///
///   - <b>!ATab[[Cc][NNN]|Reset]</b><br>
///     Inserts an "automatic tabulator stop". These are tabulator positions that are stored
///     internally and are automatically extended at the moment the actual contents exceeds the
///     currently stored tab-position. An arbitrary number of auto tab stop and field width
///     (see <b>!AWith</b> below) values is maintained by the formatter.
///
///     Which each new invocation of \alib{format;Formatter},
///     the first auto value is chosen and with each use of \c !ATab or \c !AWidth, the next value is
///     used.<br>
///     However the stored values are cleared, whenever \b %Format is invoked on a non-acquired
///     formatter! This means, to preserve the auto-positions across multiple format invocations,
///     a formatter has to be acquired explicitly before the format operations and released
///     afterwards.
///
///     Alternatively to this, the positions currently stored with the formatter can be reset with
///     providing argument \c Reset in the format string.
///
///     By default, the fill character is space <c>' '</c>. It can be changed with optional character
///     'C' plus the character wanted. The optional number provided gives the growth value by which
///     the tab will grow if its position is exceeded. This value defaults to \c 3.
///
///     Both, auto tab and auto width conversions may be used to increase readability of multiple
///     output lines. Of course, output is not completely tabular, only if those values that result
///     in the biggest sizes are formatted first. If a perfect tabular output is desired, the data
///     to be formatted may be processed twice: Once to temporary buffer which is disposed and then
///     a second time to the desired output \b %AString.
///
///   - <b>!AWidth[NNN|Reset]</b><br>
///     Increases field width with repetitive invocations of format whenever a field value did not
///     fit to the actually stored width. Optional decimal number \b NNN is added as a padding value.
///     for more information, see <b>!ATab</b> above.
///
///   - <b>!Xtinguish</b><br>
///     Does not print anything. This is useful if format strings are externalized, e.g defined
///     in \alib{camp::Camp;GetResourcePool;library resources}. Modifications of such resources
///     might use this conversion to suppress the display of arguments (which usually are
///     hard-coded).
///
///   - <b>!Replace<search><replace></b><br>
///     Searches string \p{search} and replaces with \p{replace}. Both values have to be given
///     enclosed by characters \c '<' and \c '>'. In the special case that \p{search} is empty
///     (<c><></c>), string \p{replace} will be inserted if the field argument is an empty
///     string.
///
///\I{##########################################################################################}
/// # Reference Documentation #
/// @throws <b>alib::format::FMTExceptions</b>
///   - \alib{format::FMTExceptions;ArgumentIndexOutOfBounds}
///   - \alib{format::FMTExceptions;IncompatibleTypeCode}
///   - \alib{format::FMTExceptions;MissingClosingBracket}
///   - \alib{format::FMTExceptions;MissingPrecisionValuePS}
///   - \alib{format::FMTExceptions;DuplicateTypeCode}
///   - \alib{format::FMTExceptions;UnknownTypeCode}
///   - \alib{format::FMTExceptions;ExclamationMarkExpected}
///   - \alib{format::FMTExceptions;UnknownConversionPS}
///   - \alib{format::FMTExceptions;PrecisionSpecificationWithInteger}
//==================================================================================================
class FormatterPythonStyle : public FormatterStdImpl
{
  //################################################################################################
  // Protected fields
  //################################################################################################
  protected:
    /// Set of extended placeholder attributes, needed for this type of formatter in
    /// addition to parent's \alib{format::FormatterStdImpl;PlaceholderAttributes}.
    struct PlaceholderAttributesPS
    {
        /// The portion of the replacement field that represents the conversion specification.
        /// This specification is given at the beginning of the replacement field, starting with
        /// \c '!'.
        Substring           Conversion;
 
        /// The position where the conversion was read. This is set to \c -1 in #resetPlaceholder.
        int                 ConversionPos;
 
 
        /// The value read from the precision field.   This is set to \c -1 in #resetPlaceholder.
        int                 Precision;
 
        /// The position where the precision was read. This is set to \c -1 in #resetPlaceholder.
        int                 PrecisionPos;
 
        /// The default precision if not given.
        /// This is set to \c 6 in #resetPlaceholder, but is changed when specific.
        int                 DefaultPrecision;
    };
 
    /// The extended placeholder attributes.
    PlaceholderAttributesPS placeholderPS;
 
  //################################################################################################
  // Public fields
  //################################################################################################
  public:
    /// Storage of sizes for auto-tabulator feature <b>{!ATab}</b> and auto field width feature
    /// <b>{!AWidth}</b>
    AutoSizes*                  Sizes;
 
    /// The default instance of field #Sizes. This might be replaced with an external object.
    AutoSizes                   SizesDefaultInstance;
 
  //################################################################################################
  //  Constructor/Destructor
  //################################################################################################
  public:
    /// Constructs this formatter.
    /// Inherited field #DefaultNumberFormat is initialized to meet the formatting defaults of
    /// Python.
    ALIB_DLL
    FormatterPythonStyle();
 
    /// Clones and returns a copy of this formatter.
    ///
    /// If the formatter attached to field
    /// \alib{format;Formatter::Next} is of type \b %FormatterStdImpl, then that
    /// formatter is copied as well.
    ///
    /// @returns An object of type \b %FormatterPythonStyle and with the same custom settings
    ///          than this.
    ALIB_DLL virtual
    SPFormatter         Clone()                                                            override;
 
    /// Resets #AutoSizes.
    /// @return An internally allocated container of boxes that may be used to collect
    ///         formatter arguments.
    virtual BoxesMA&    Reset()              override { Sizes->Reset(); return Formatter::Reset(); }
 
 
  //################################################################################################
  //  Implementation of FormatterStdImpl interface
  //################################################################################################
  protected:
    /// Sets the actual auto tab stop index to \c 0.
    virtual void        initializeFormat()                            override { Sizes->Restart(); }
 
 
 
    /// Invokes parent implementation and then applies some changes to reflect what is defined as
    /// default in the Python string format specification.
    ALIB_DLL
    virtual void        resetPlaceholder()                                                 override;
 
    /// Searches for \c '{' which is not '{{'.
    ///
    /// @return The index found, -1 if not found.
    ALIB_DLL
    virtual integer     findPlaceholder()                                                  override;
 
    /// Parses placeholder field in python notation. The portion \p{format_spec} is not
    /// parsed but stored in member
    /// \alib{format::FormatterStdImpl::PlaceholderAttributes;FormatSpec}.
    ///
    /// @return \c true on success, \c false on errors.
    ALIB_DLL
    virtual bool        parsePlaceholder()                                                 override;
 
    /// Parses the format specification for standard types as specified in
    /// \https{"Format Specification Mini Language",docs.python.org/3.5/library/string.html#format-specification-mini-language}.
    ///
    /// @return \c true on success, \c false on errors.
    ALIB_DLL
    virtual bool        parseStdFormatSpec()                                               override;
 
    /// Implementation of abstract method
    /// \alib{format;FormatterStdImpl::writeStringPortion}.<br>
    /// While writing, replaces \c "{{" with \c "{" and \c "}}" with \c "}" as well as
    /// standard codes like \c "\\n", \c "\\r" or \c "\\t" with corresponding ascii codes.
    ///
    /// @param length The number of characters to write.
    ALIB_DLL
    virtual void        writeStringPortion( integer length )                               override;
 
    /// Processes "conversions" which are specified with \c '!'.
    ///
    /// @param startIdx  The index of the start of the field written in #targetString.
    ///                  \c -1 indicates pre-phase.
    /// @param target    The target string, only if different from field #targetString, which
    ///                  indicates intermediate phase.
    /// @return \c false, if the placeholder should be skipped (nothing is written for it).
    ///         \c true otherwise.
    ALIB_DLL
    virtual bool        preAndPostProcess( integer   startIdx,
                                           AString*  target     )                          override;
 
 
    /// Makes some attribute adjustments and invokes standard implementation
    /// @return \c true if OK, \c false if replacement should be aborted.
    ALIB_DLL
    virtual bool        checkStdFieldAgainstArgument()                                     override;
};
} // namespace [alib::format]
 
ALIB_EXPORT namespace alib {
/// Type alias in namespace \b alib.
using  FormatterPythonStyle=   format::FormatterPythonStyle;
}