Parsing Arguments (GNU Octave (version 6.4.0))

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#### 11.9.3 Parsing Arguments

If none of the preceding validation functions is sufficient there is also the class `inputParser` which can perform extremely complex input checking for functions.

: p = inputParser ()

  Create object p of the inputParser class.

  This class is designed to allow easy parsing of function arguments. The class supports four types of arguments:

  1. mandatory (see `addRequired`);
  2. optional (see `addOptional`);
  3. named (see `addParameter`);
  4. switch (see `addSwitch`).

  After defining the function API with these methods, the supplied arguments can be parsed with the `parse` method and the parsing results accessed with the `Results` accessor.

: inputParser.Parameters

  Return list of parameter names already defined.

: inputParser.Results

  Return structure with argument names as fieldnames and corresponding values.

: inputParser.Unmatched

  Return structure similar to `Results`, but for unmatched parameters. See the `KeepUnmatched` property.

: inputParser.UsingDefaults

  Return cell array with the names of arguments that are using default values.

: inputParser.CaseSensitive = boolean

  Set whether matching of argument names should be case sensitive. Defaults to false.

: inputParser.FunctionName = name

  Set function name to be used in error messages; Defaults to empty string.

: inputParser.KeepUnmatched = boolean

  Set whether an error should be given for non-defined arguments. Defaults to false. If set to true, the extra arguments can be accessed through `Unmatched` after the `parse` method. Note that since `Switch` and `Parameter` arguments can be mixed, it is not possible to know the unmatched type. If argument is found unmatched it is assumed to be of the `Parameter` type and it is expected to be followed by a value.

: inputParser.StructExpand = boolean

  Set whether a structure can be passed to the function instead of parameter/value pairs. Defaults to true.

  The following example shows how to use this class:

      function check (varargin)
        p = inputParser ();                      # create object
        p.FunctionName = "check";                # set function name
        p.addRequired ("pack", @ischar);         # mandatory argument
        p.addOptional ("path", pwd(), @ischar);  # optional argument

        ## create a function handle to anonymous functions for validators
        val_mat = @(x) isvector (x) && all (x <= 1) && all (x >= 0);
        p.addOptional ("mat", [0 0], val_mat);

        ## create two arguments of type "Parameter"
        val_type = @(x) any (strcmp (x, {"linear", "quadratic"}));
        p.addParameter ("type", "linear", val_type);
        val_verb = @(x) any (strcmp (x, {"low", "medium", "high"}));
        p.addParameter ("tolerance", "low", val_verb);

        ## create a switch type of argument
        p.addSwitch ("verbose");

        p.parse (varargin{:});  # Run created parser on inputs

        ## the rest of the function can access inputs by using p.Results.
        ## for example, get the tolerance input with p.Results.tolerance
      endfunction

      check ("mech");           # valid, use defaults for other arguments
      check ();                 # error, one argument is mandatory
      check (1);                # error, since ! ischar
      check ("mech", "~/dev");  # valid, use defaults for other arguments

      check ("mech", "~/dev", [0 1 0 0], "type", "linear");  # valid

      ## following is also valid.  Note how the Switch argument type can
      ## be mixed into or before the Parameter argument type (but it
      ## must still appear after any Optional argument).
      check ("mech", "~/dev", [0 1 0 0], "verbose", "tolerance", "high");

      ## following returns an error since not all optional arguments,
      ## 'path' and 'mat', were given before the named argument 'type'.
      check ("mech", "~/dev", "type", "linear");

  Note 1: A function can have any mixture of the four API types but they must appear in a specific order. `Required` arguments must be first and can be followed by any `Optional` arguments. Only the `Parameter` and `Switch` arguments may be mixed together and they must appear at the end.

  Note 2: If both `Optional` and `Parameter` arguments are mixed in a function API then once a string Optional argument fails to validate it will be considered the end of the `Optional` arguments. The remaining arguments will be compared against any `Parameter` or `Switch` arguments.

  See also: nargin, validateattributes, validatestring, varargin.

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