util::fhicl Namespace Reference

Classes
struct	SequenceWrapper
	Helper to return a converted sequence from FHiCL configuration. More...

Functions
template<typename Optional >
std::optional< typename Optional::value_type >	getOptionalValue (Optional const &parameter)
	Returns the value of an optional parameter as std::optional. More...
template<typename T , typename Optional >
T	getOptionalValue (Optional const &parameter, T defValue)
	Returns the value of an optional parameter, or a default value. More...

Function Documentation

template<typename Optional >

std::optional< typename Optional::value_type > util::fhicl::getOptionalValue

(

Optional const &

parameter

)

Returns the value of an optional parameter as std::optional.

Template Parameters

Optional

FHiCL optional class (e.g. fhicl::OptionalAtom)

Parameters

parameter

the optional FHiCL parameter

Returns

the value of the parameter

This utility allows to carry the information whether an optional parameter was specified or not. It may also help with single-line initialization of data members from FHiCL optional parameters, e.g.

struct Config {

  fhicl::Atom<unsigned int> A {
    fhicl::Name("A"),
    fhicl::Comment("parameter A")
    };

  fhicl::OptionalAtom<unsigned int> B {
    fhicl::Name("B"),
    fhicl::Comment("parameter B (default: same as A)")
    };

};

unsigned int fA, fB;

MyClass(Config const& config)
  : fA(config.A())
  , fB(util::fhicl::getOptionalValue(config.B).value_or(fA))
  {}

This feature will be rendered obsolete by Redmine Issue #23653.

Definition at line 188 of file FHiCLutils.h.

                                                     {

  using Value_t = typename Optional::value_type;

  if (!parameter.hasValue()) return std::nullopt;

  Value_t value;
  parameter(value);
  return { value };

} // util::fhicl::getOptionalValue(Optional& parameter)

template<typename T , typename Optional >

T util::fhicl::getOptionalValue	(	Optional const &	parameter,
		T	defValue
	)

Returns the value of an optional parameter, or a default value.

Template Parameters

T	type of the value being returned
Optional	FHiCL optional class (e.g. fhicl::OptionalAtom)

Parameters

parameter	the optional FHiCL parameter
defValue	default value to be returned

Returns

the value of the parameter, or defValue if absent

It is usually preferable to use a non-optional FHiCL parameter with a default value, but some types are not well suited for this. Also, this function does not buy much unless the parameter reading needs to be done in a single statement, like in the initialization list of a constructor:

struct Config {

  fhicl::OptionalSequenceTable<BoardCfg> Boards {
    fhicl::Name("MyStruct"),
    fhicl::Comment("data configuration elements")
    };

};

using AllBoardCfg_t = std::vector<BoardCfg>;

AllBoardCfg_t fBoards;


MyClass(Config const& config)
  : fBoards
    (util::fhicl::getOptionalValue<BoardCfg>(config.Boards, AllBoardCfg_t{}))
  {}

Definition at line 203 of file FHiCLutils.h.

  { parameter(defValue); return defValue; }