Fhiclcpp types in detail » History » Version 31

Version 30 (Kyle Knoepfel, 11/17/2015 12:37 PM) → Version 31/56 (Kyle Knoepfel, 11/17/2015 12:37 PM)

h1. @fhiclcpp@ types in detail

* [[Fhiclcpp_types_in_detail#ctors|Parameter constructors]]
** [[Fhiclcpp_types_in_detail#ctors_rules|General rules]]
** [[Fhiclcpp_types_in_detail#atom|Atom<T>]]
** [[Fhiclcpp_types_in_detail#vector|Sequence<T>]]
*** [[Fhiclcpp_types_in_detail#make_empty|make_empty()]]
*** [[Fhiclcpp_types_in_detail#narrowing|Caveat regarding narrowing conversions]]
** [[Fhiclcpp_types_in_detail#array|Sequence<T,std::size_t>]]
** [[Fhiclcpp_types_in_detail#tuple|Tuple<T...>]]
** [[Fhiclcpp_types_in_detail#table|Table<T>]]
* [[Fhiclcpp_types_in_detail#return|Return types]]
* [[Fhiclcpp_types_in_detail#table_func|Additional functions for Table<T>]]
** [[Fhiclcpp_types_in_detail#get_pset|get_PSet]]
** [[Fhiclcpp_types_in_detail#print|print_allowed_configuration]]
** [[Fhiclcpp_types_in_detail#validate|validate_ParameterSet (*expert*)]]
* [[Fhiclcpp_types_in_detail#common_acc|Common parameter accessors]]


h1(#ctors). Parameter constructors

h2(#ctors_rules). %{color:blue}General rules%

For each of the @fhiclcpp@ types, the following rules apply:
* The @Name@ argument is required.
* If there is more than one argument, the @Name@ argument must be first in the list.
* If there are three arguments, the relative order of the @Comment@ argument and default-value argument is not important.
<pre><code class="cpp">
Atom<int> val { Name("val"), Comment("Some parameter"), 9 }; // is equivalent to
Atom<int> val { Name("val"), 9, Comment("Some parameter") };
* The @Table<T>@ parameter does not support a default value.

h2(#atom). %{color:blue}@Atom<T>@%

<pre><code class="cpp">
Atom<int> var { Name("var") };
Atom<int> var { Name("var"), 9 };
Atom<int> var { Name("var"), Comment("A parameter description") };
Atom<int> var { Name("var"), Comment("A parameter description"), 9 };

h2(#vector). %{color:blue}@Sequence<T>@%

This class template is used for unbounded sequences. See the two caveats below.

<pre><code class="cpp">
Sequence<int> seq { Name("seq") };
Sequence<int> seq { Name("seq"), Comment("A sequence") };
Sequence<int> seq { Name("seq"), Sequence<int>{ 4, 5, 6, 7 } };
Sequence<int> seq { Name("seq"), { 4, 5, 6, 7 } };
Sequence<int> seq { Name("seq"), Comment("A sequence"), Sequence<int>{ 4, 5, 6, 7 } };
Sequence<int> seq { Name("seq"), Comment("A sequence"), { 4, 5, 6, 7 } };

h3(#make_empty). @Sequence<T>::make_empty()@

Due to the implementation details of the unbounded sequence, the following:

<pre><code class="cpp">
Sequence<int> seq { Name("seq"), Sequence<int>{} }; // Don't do this.

_does not_ represent an empty sequence. If you would like an empty sequence as a default value, use the following:

<pre><code class="cpp">
Sequence<int> seq { Name("seq"), Sequence<int>::make_empty() };

h3(#narrowing). Precaution regarding narrowing conversions and @std::initializer_list@ objects

The following configuration will trigger a compilation warning:

<pre><code class="cpp">
Sequence<int> seq1 { Name("seq1"), Sequence<int>{ 1, 2.4e-4 } };
Sequence<int> seq2 { Name("seq2"), { 1, 2.4e-4 } };

that looks similar to this:

warning: narrowing conversion of ‘2.4000000000000001e-4’ from ‘double’ to ‘int’ inside { } [-Wnarrowing]

For build systems that convert compile-time warnings to errors, this will result in a build failure. The warning results from the nature of an @std::initializer_list@ object, signified by @'{1, 2.4e-4}'@, which is used to initialize the sequence objects. For @std::initializer_list@ objects, narrowing conversions are not allowed--that is, converting a @double@ to an @int@ is an example of narrowing that results in loss of information. This is the most likely example of where you may find a narrowing conversion.

h2(#array). %{color:blue}@Sequence<T,std::size_t>@%

This class template is used for sequences of a specific length, known at compile time.

<pre><code class="cpp">
Sequence<int,3u> seq { Name("seq") };
Sequence<int,3u> seq { Name("seq"), Comment("A sequence") };
Sequence<int,3u> seq { Name("seq"), Sequence<int,3u>{ 4, 5, 6 } };
Sequence<int,3u> seq { Name("seq"), { 4, 5, 6 } };
Sequence<int,3u> seq { Name("seq"), Comment("A sequence"), Sequence<int,3u>{ 4, 5, 6 } };
Sequence<int,3u> seq { Name("seq"), Comment("A sequence"), { 4, 5, 6 } };

The warning regarding narrowing conversions [[Fhiclcpp_types_in_detail#narrowing|above]] applies for bounded sequences as well.

h2(#tuple). %{color:blue}@Tuple<T...>@%

<pre><code class="cpp">
Tuple<string,bool> tuple { Name("tuple") };
Tuple<string,bool> tuple { Name("tuple"), Comment("A tuple") };
Tuple<string,bool> tuple { Name("tuple"), Tuple<string,bool>{"explicit?", true} };
Tuple<string,bool> tuple { Name("tuple"), {"compact?", true } };
Tuple<string,bool> tuple { Name("tuple"), Comment("A tuple"), Tuple<string,bool>{ "Particle physics is neat.", true } };
Tuple<string,bool> tuple { Name("tuple"), Comment("A tuple"), { "This is false", false } };

h2(#table). %{color:blue}@Table<T>@%

<pre><code class="cpp">
Table<T> config { Name("config") };
Table<T> config { Name("config"), Comment("This describes the table") };


h1(#return). Return types

|{background:#fba}. *@fhiclcpp@ parameter*|{background:#fba}. *Function call*|{background:#fba}. *Return type*|
|\3{background:#ddd}. _Simple @fhiclcpp@ parameters_|
|@Atom<std::string> label@; |@label()@| @std::string const&@|
|/2.@Sequence<int> counts@; | @counts()@ | @std::vector<int>@|
|@counts(1)@ | @int@ |
|/2.@Sequence<double, 3u> point@;| @point()@ | @std::array<double, 3u>@|
|@point(0)@ | @double@ |
|/3.@Tuple<std::string, double> assoc;@|@assoc()@| @std::tuple<std::string, double>@|
|@Table<Config> config;@|@config()@|@Config const&@|
|\3{background:#ddd}. _Nested @fhiclcpp@ parameters_|
|/2.@Sequence< Sequence<int> > datasets;@ | @datasets()@ | @std::vector< std::vector<int> >@ |
| @datasets(17)@ | @std::vector<int>@ |
|/2.@Sequence< Sequence<int>, 2u > twoDatasets;@ | @twoDatasets()@ | @std::array< std::vector<int>, 2u >@ |
|@twoDatasets(1)@ | @std::vector<int>@ |
|/2.@Sequence< Sequence<int, 2u> > intPairs;@ | @intPairs()@ | @std::vector< std::array<int, 2u> >@ |
|@intPairs(42)@ | @std::array<int, 2u>@|
|/2.@Sequence< Tuple<std::string, int, bool> > triplets;@ | @triplets()@ | @std::vector< std::tuple<std::string, int, bool> >@ |
|@triplets(3)@ | @std::tuple<std::string, int, bool>@ |
|/2.@Sequence< Table<Config> > manyConfigTables;@ | @manyConfigTables()@ | @std::vector< Config >@ |
|@manyConfigTables(6)@ | @Config const&@ |
|/5.@Tuple< std::string, Table<Config> > configAssoc;@ | @configAssoc()@ | @std::tuple< std::string, Config >@ |
|@configAssoc.get<0>()@ | @std::string@ |
|@configAssoc.get<std::string>()@ | @std::string@ |
|@configAssoc.get<1>()@ | @Config@ |
|@configAssoc.get< Table<Config> >()@ | @Config@ |
|/3.@Tuple< Tuple<std::string,bool>, Sequence<int> > awkward;@ | @awkward()@ | @std::tuple< std::tuple<std::string, bool>, std::vector<int> >@ |


h1(#table_func). Additional functions for @Table<T>@

The @Table@ template offers a few extra functions that the user can call:

<pre><code class="cpp">
fhicl::ParameterSet const& get_PSet() const;

void print_allowed_configuration(std::ostream& os,
std::string const& tab = std::string(3,' ') ) const;

// Expert-level functions
void validate_ParameterSet(fhicl::ParameterSet const& pset,
std::set<std::string> const& keysToIgnore = {} );


h3(#get_pset). @get_PSet@

A call to this function returns a @const@ reference to the @ParameterSet@ object that was used to fill the values of the individual @Table@ members. This is helpful for users who need to interact with the @ParameterSet@ object itself.

h3(#print). @print_allowed_configuration@

For any @Table<Config>@ object, @print_allowed_configuration@ will fill a user-supplied @std::ostream@ object with the allowed configuration as defined by the @Config@ struct. The optional second argument specifies the number of spaces per indentation. The default is 3 spaces but is, of course, user-configurable.


%{color:red} _[ *N.B.* The following function should not normally be invoked by users. It is meant to be called only in contexts outside of @art@. Please consult for guidance.]_%

h3(#validate). @validate_ParameterSet@ (expert)

This function is intended for experts who need to validate the @pset@ object themselves. The @keysToIgnore@ variable represents a set of keys for which the validation step will ignore. The validation function will ignore any nested keys as well--i.e. if a user specifies an ignorable key as @table1@, the (e.g.) @table1.someAtom@ key would be ignored in addition to just the @table1@ name. An indexed parameter (e.g.) @seq[1]@ is considered a nested parameter of its parent @seq@. Providing or not providing the ignorable key in a configuration will lead to no error upon validation of the @ParameterSet@.

Should the validation step fail, an exception is thrown of type @fhicl::detail::validationException@. This behavior is not currently configurable.


h1(#common_acc). Common parameter accessors

Each of the @fhiclcpp@ types has the following accessors:
<pre><code class="cpp">
std::string key() const;
std::string name() const;
std::string comment() const;
bool has_default() const;
bool is_optional() const;
par_type parameter_type() const;

To call these functions, the difference in syntax is crucial:

<pre><code class="cpp">
Atom<int> val { Name("val") };

auto key1 = val.key(); // correct
auto key2 = val().key(); // ! compile-time ERROR - 'val()' is an int, which has no accessor called 'key()'

h2. @key()@

A call to @key()@ returns the _full_ key, including all enclosing tables. For example, consider a module that is designed to allow the following configuration:
<pre><code class="ruby">
pset: {
list: [ { particle: electron },
{ particle: muon } ]
</code></pre>For a suitably declared set of @fhiclcpp@ parameters, the returned key corresponding to "muon" would be @pset.list[1].particle@.

h2. @name()@

The name is the most-nested name in the key. For the above "muon" parameter, a key of @pset.list[1].particle@ has a corresponding name of @particle@. If the parameter in question were @pset.list[1]@, the name would be[1] @list[1]@.

fn1. Technically, this is inaccurate -- sequence elements do not have names. However, for the sake of parameter identification, a sequence element has a name whose value is the sequence name with the appropriate sequence element index/indices appended.

%{color:red} *N.B.*% The returned value is different than the _relative_ name that is supplied in the @Name("val")@ argument to the @fhiclcpp@ parameter constructor.

h2. @comment()@

Returns the comment supplied as the string literal in (e.g.) @Comment("Here is the comment")@. If no @Comment@ argument is provided in the @fhiclcpp@ parameter constructor, a call to this function returns an empty string.

h2. @has_default()@

Returns @true@ or @false@ depending on whether the user supplied a default value for the parameter.

h2. @is_optional()@

Returns @true@ or @false@ depending on whether the parameter is of an @Optional*@ @fhiclcpp@ type.

h2. @parameter_type()@

Returns an enumeration value based on the parameter type:

<pre><code class="cpp">
enum class par_type {
ATOM, // (Optional)Atom<T>
TABLE, // (Optional)Table<T>
SEQ_VECTOR, // (Optional)Sequence<T>
SEQ_ARRAY, // (Optional)Sequence<T,std::size_t>
TUPLE, // (Optional)Tuple<T...>
NTYPES // Signifies invalid parameter