DefaultHelpPrinter

DefaultHelpPrinter is the help renderer that argparse uses out of the box. It implements HelpPrinter and is the class to derive from in order to customize help screen.

Public data members

config

DefaultHelpPrinter.config holds a config object that was passed to constructor.

style

DefaultHelpPrinter.style holds an actual style that should be applied to the help screen text. This should be used instead of config.style.

Public member functions

Constructor

Constructor of DefaultHelpPrinter initializes an object with specified Config and Style parameters.

Signature

this(const Config config, Style style)

formatCommandUsage

formatCommandUsage returns formatted string for command usage line which is usually Usage: ....

Signature

string formatCommandUsage(string[] commandName, in CommandHelpInfo helpInfo)

Parameters

commandName
List of command names including names of parent commands starting with top-level command.
helpInfo
Help info about command.

Return value

String with formatted usage info.

formatArgumentUsage

formatArgumentUsage returns formatted string for argument usage (argument representation in command usage line) which is usually string like [--foo FOO].

Signature

string formatArgumentUsage(in ArgumentHelpInfo helpInfo, bool usageString)

Parameters

helpInfo
Help info about argument.
usageString
If true then the returned value wil be used in usage string, otherwise in argument description.

Return value

String with formatted argument usage info.

formatArgumentValue

formatArgumentValue returns formatted string for argument value: --name <value>. For example, it returns [FOO ...] if argument usage is --foo [FOO ...].

Signature

string formatArgumentValue(in ArgumentHelpInfo helpInfo)

Parameters

helpInfo
Help info about argument.

Return value

String with formatted argument value.

formatArgumentDescription

formatArgumentDescription returns the description of an argument that is printed next to its name, including the default value of the argument if it should be printed. For example, it returns path to config (default: /etc/app.conf) for an argument that is described as path to config and has /etc/app.conf default value.

Signature

string formatArgumentDescription(in ArgumentHelpInfo helpInfo)

Parameters

helpInfo
Help info about argument.

Return value

String with formatted argument description.

formatArgumentList

formatArgumentList returns a list of arguments formatted the same way the help screen formats them: every argument takes a line with its usage on the left and its description on the right, aligned into two columns and wrapped when needed. It is useful to spell out which arguments a message is about, for example:

  --input INPUT    File to read the data from
  destination      Where to upload the result

Signature

string formatArgumentList(const ArgumentHelpInfo[] args)

Parameters

args
Arguments to be listed.

Return value

String with the formatted list of arguments. Every line, including the last one, is terminated with \n. Empty string if args is empty.

createHelpScreen

This function creates HelpScreen based on list of commands.

Signature

HelpScreen createHelpScreen(CommandHelpInfo[] commands)

Parameters

commands
Current stack of (sub)commands starting with top-level command.

Return value

HelpScreen object with all information about help screen.

createSubCommandGroup

Function that creates a HelpScreen.Group group from CommandHelpInfo data.

Signature

HelpScreen.Group createSubCommandGroup(const ref CommandHelpInfo cmd)

Parameters

cmd
Command that contains subcommands.

Return value

HelpScreen.Group object with subcommand entries.

createArgumentsGroups

Function that creates an array of HelpScreen.Group groups from commands data. Usually this function merges groups with the same names from all commands.

Signature

HelpScreen.Group[] createArgumentsGroups(const ref CommandHelpInfo[] commands)

Parameters

commands
Current stack of (sub)commands starting with top-level command.

Return value

Array of HelpScreen.Group objects representing groups of arguments.

printHelp

Function that creates help screen from commands info and prints through sink.

Signature

void printHelp(void delegate(string) sink, CommandHelpInfo[] commands)

Parameters

sink
Delegate that receives output in pieces.
commands
Current stack of (sub)commands starting with top-level command.

printHelpScreen

This function prints HelpScreen object through sink.

Signature

void printHelpScreen(void delegate(string) sink, const ref HelpScreen screen, size_t descriptionOffset)

Parameters

sink
Delegate that receives output in pieces.
screen
Help information to print.
descriptionOffset
Screen offset for parameter description. If help text can be represented as two columns of text, descriptionOffset is the position when the second column should start.

printGroup

This function prints HelpScreen.Group object through sink.

Signature

void printGroup(void delegate(string) sink, const ref HelpScreen.Group group, size_t descriptionOffset)

Parameters

sink
Delegate that receives output in pieces.
group
Group of parameters to print.
descriptionOffset
Screen offset for parameter description. If help text can be represented as two columns of text, descriptionOffset is the position when the second column should start.

printParameter

This function prints HelpScreen.Parameter object through sink.

Signature

  void printParameter(void delegate(string) sink, const ref HelpScreen.Parameter param, size_t descriptionOffset)

Parameters

sink
Delegate that receives output in pieces.
param
Parameter to print.
descriptionOffset
Screen offset for parameter description. If help text can be represented as two columns of text, descriptionOffset is the position when the second column should start.

Public static functions

wrapText

wrapText function wraps text into paragraphs by breaking it up into asequence of lines separated with \n, such that the length of each line does not exceed specific limit. The last line is terminated with \n.

This function is similar to std.string.wrap but with few adjustments:

Styling, if any, is removed during calculation of word length.
Line breaks \n are preserved. This allows having line breaks where needed in addition to those that are added by function itself.
Output is returned via sink in parts rather than in allocated string. Caller can use appender!string if string is needed.

Signature

static void wrapText(void delegate(string) sink,
    string text,
    string firstIndent,
    string indent,
    size_t maxLineLength = 80)

Parameters

sink
Delegate that receives output in pieces.
text
Text to be wrapped.
firstIndent
String used to indent first line.
indent
String used to indent second and following lines.
maxLineLength
Maximum line length.

Last modified: 11 September 2026