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There are uniform requirements for the template parameters across itl's class templates. The template parameters can be grouped with respect to those requirements.

used in 
Kind 
Parameter 
Instance 
Description 

Domain order 




For the type 






Interval type 





Codomain aggregation 




For the type 

















Intersection is propagated to CodomainT values via functor 
Memory allocation 




An allocator can be chosen for memory allocation. 
The next table gives an overview over the requirements for template parameter
DomainT
. Some requirements
are dependent on conditions. Column operators
shows the operators and functions that are expected for DomainT
,
if the default order Compare = std::less
is used.
Parameter 
Condition 
Operators 
Requirement 













A domain type DomainT
for
intervals and interval containers has to satisfy the requirements of concept
Regular
which implies among other
properties the existence of a copy and a default constructor. In addition
IsIncrementable
or HasUnon
is required for DomainT
.
In the itl we represent an empty interval
by a closed interval [b,a]
where a <
b
(here <
represents Compare<DomainT>()
).
To construct one of these empty intervals as default constructor for any
type DomainT
we choose [1,0]
, where
0
is a nullvalue or neutron
and 1
is a onevalue or unon
:
interval() := [unon<DomainT>::value(), neutron<DomainT>::value()] //pseudocode
Neutrons
are implemented
via call of the default constructor of DomainT
.
An unon<T>::value()
is implemented by default
as
a neutron
, that is incremented
once.
template <class Type> inline Type unon<Type>::value(){ return succ(neutron<Type>::value()); };
So a type DomainT
that is
incrementable
will also have
an unon
. If it does not,
an unon
can be provided.
An unon
can be any value,
that is greater as the neutron
value in the Compare
order
given. An example of a type, that has a neutron
but no increment is string
.
So for std::string
an unon is implemented like this:
// Smallest 'visible' string that is greater than the empty string. template <> inline std::string unon<std::string>::value(){ return std::string(" "); };
Just as for the key type of std::sets and maps template parameter Compare
is required to be a strict
weak ordering on DomainT
.
Finally, if DomainT
is an
integral type, DomainT
needs
to be incrementable
and
decrementable
. This 'bicrementability'
needs to be implemented on the smallest possible unit of the integral type.
This seems like being trivial but there are types like e.g. boost::date_time::ptime
, that are integral in nature but
do not provide the required in and decrementation on the least incrementable
unit. For itl::intervals
incementation and decementation is used for computations between open to
closed interval borders like e.g. [2,43) == [2,42]
. Such computations always need only one
in or decrementation, if DomainT
is an integral type.
Requirements on the Interval
parameter are closely related to the DomainT
parameter. template Interval
has two template parameters itself for an element type and a compare order
and it is of course internally always instantiated as Interval<DomainT,Compare>
. Interval<DomainT,Compare>
then has to implement an order called
exclusive_less
. Two intervals
x,
y
are exclusive_less
x.exclusive_less(y)
if all DomainT
elements of
x
are less than elements
of y
in the Compare
order.
Parameter 
Operators 
Requirement 




Summarized in the next table are requirements for template parameter CodomainT
of associated values for Maps
. Again there are conditions
for some of the requirements. Column operators contains
the operators and functions required for CodomainT
,
if we are using the default combiner Combine
= itl::inplace_plus
.
Parameter 
Condition 
Operators 
Requirement 










only 



... and also 






The requirements on the type CodomainT
of associated values for a itl::map
or interval_map
depend
on the usage of their aggregation functionality. If aggregation on overlap
is never used, that is to say that none of the addition, subtraction and
intersection operations (+, +=, add
,
, =,
subtract
, &, &=, add_intersection)
are used on the interval_map
,
then CodomainT
only needs
to be Regular.
Regular object semantics
implies DefaultConstructible
and EqualityComparable
which
means it has a default ctor CodomainT()
and an operator
==
.
Use interval_maps
without aggregation,
if the associated values are not addable but still are attached to intervals
so you want to use interval_maps
to handle them. As long as those values are added with insert
and deleted with erase
interval_maps
will work fine with
such values.
If only addition is
used via interval_map's
+, +=
or add
but no subtraction,
then CodomainT
need to be
Combinable
for functor template
Combine
. That means in most
cases when the default implementation inplace_plus
for Combine
is used, that
CodomainT
has to implement
operator +=
.
For associated value types, that are addable but not subtractable like e.g.
std::string
it usually makes sense to use addition
to combine values but the inverse combination is not desired.
interval_map<int,std::string> cat_map; cat_map += make_pair(interval<int>::rightopen(1,5),std::string("Hello")); cat_map += make_pair(interval<int>::rightopen(3,7),std::string(" world")); cout << "cat_map: " << cat_map << endl; //cat_map: {([1,3)>Hello)([3,5)>Hello world)([5,7)> world)}
For complete aggregation functionality an inverse aggregation
functor on a Map
's CodomainT
is needed. The itl provides a
metafunction inverse
for
that purpose. Using the default Combine
= inplace_plus
that relies on the existence of operator
+=
on type CodomainT
metafunction inverse
will
infer inplace_minus
as inverse functor, that requires operator
=
on type CodomainT
.
In the itl's design we make the assumption, in particular for the default
setting of parameters Combine =
inplace_plus
,
that type CodomainT
has a
neutral element or neutron
with respect to the Combine
functor.