...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Copyright © 2003-2004 Thorsten Ottosen
Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see http://www.boost.org/LICENSE_1_0.txt).
operator+=()
operator()()
list_of()
map_list_of()
tuple_list_of()
repeat()
and repeat_fun()
ref_list_of()
and cref_list_of()
ptr_push_back(), ptr_push_front()
and ptr_insert()
ptr_list_of()
list_of()
and map_list_of()
repeat()
and repeat_fun()
list_inserter
make_list_inserter()
There appear to be few
practical uses of operator,()
.
Bjarne
Stroustrup, The Design and Evolution of C++
The purpose of this
library is to make it easy to fill containers with data by overloading
operator,()
and operator()()
. These two operators
make it possible to construct lists of values that are then copied into a
container:
vector<int> v; v += 1,2,3,4,5,6,7,8,9;
map<string,int> m; insert( m )( "Bar", 1 )( "Foo", 2 );
These lists are particularly useful in learning, testing, and prototyping situations, but can also be handy otherwise. The library comes with predefined operators for the containers of the standard library, but most functionality will work with any standard compliant container. The library also makes it possible to extend user defined types so for example a member function can be called for a list of values instead of its normal arguments.
Within two minutes you should be able to use this library. The main components are explained in these sections:
operator+=()
operator()()
list_of()
map_list_of()
tuple_list_of()
repeat()
and repeat_fun()
ref_list_of()
and cref_list_of()
ptr_push_back(), ptr_push_front()
and ptr_insert()
ptr_list_of()
operator+=()
To fill a vector (or any standard container) with values using
operator+=()
you write
Here we only stuffed constants into the container, but the list can consists of arbitrary expressions as long as the result of each expression is convertible to the#include <boost/assign/std/vector.hpp> // for 'operator+=()' #include <boost/assert.hpp>; using namespace std; using namespace boost::assign; // bring 'operator+=()' into scope { vector<int> values; values += 1,2,3,4,5,6,7,8,9; // insert values at the end of the container BOOST_ASSERT( values.size() == 9 ); BOOST_ASSERT( values[0] == 1 ); BOOST_ASSERT( values[8] == 9 ); }
value_type
of the container.
operator()()
We do not call operator()()
directly, but instead we call a
function that returns a proxy-object that defines operator()()
.
The function that returns the proxy object is always named after the member
function that is used to copy the values in the list into the container.
So to fill a map with pairs of values you write
Note that#include <boost/assign/list_inserter.hpp> // for 'insert()' #include <boost/assert.hpp> #include <string> using namespace std; using namespace boost::assign; // bring 'insert()' into scope { map<string,int> months; insert( months ) ( "january", 31 )( "february", 28 ) ( "march", 31 )( "april", 30 ) ( "may", 31 )( "june", 30 ) ( "july", 31 )( "august", 31 ) ( "september", 30 )( "october", 31 ) ( "november", 30 )( "december", 31 ); BOOST_ASSERT( months.size() == 12 ); BOOST_ASSERT( months["january"] == 31 ); }
operator()()
is much more handy when
we need to construct objects using several arguments
(up to five arguments are supported by default, but the limit can be customized).
This is also true for sequences:
Besides#include <boost/assign/list_inserter.hpp> // for 'push_front()' #include <boost/assert.hpp> #include <string> #include <utility> using namespace std; using namespace boost::assign; // bring 'push_front()' into scope { typedef pair< string,string > str_pair; deque<str_pair> deq; push_front( deq )( "foo", "bar")( "boo", "far" ); BOOST_ASSERT( deq.size() == 2 ); BOOST_ASSERT( deq.front().first == "boo" ); BOOST_ASSERT( deq.back().second == "bar" ); }
push_front()
we could also have used
push_back()
if the container has a corresponding member
function. Empty parentheses can be used to insert default-constructed
objects, for example,
push_front( deq )()()
will insert two default-constructed
str_pair
objects.
If operator()()
is too cumbersome to use with eg.
push_front()
we can also say
deque<int> di; push_front( di ) = 1,2,3,4,5,6,7,8,9; BOOST_ASSERT( di.size() == 9 ); BOOST_ASSERT( di[0] == 9 );
Just to make it perfectly clear, the code above is not restricted to the
standard containers, but will work with all standard compliant containers
with the right member function. It is only operator+=()
that has been restricted to
the standard containers.
list_of()
list_of()
comes into play. With list_of()
we can create anonymous lists that automatically converts to
any container:
If we need to initialize a container adapter, we need to help the compiler a little by calling#include <boost/assign/list_of.hpp> // for 'list_of()' #include <boost/assert.hpp> #include <list> #include <stack> #include <string> using namespace std; using namespace boost::assign; // bring 'list_of()' into scope { const list<int> primes = list_of(1)(2)(3)(5)(7)(11); BOOST_ASSERT( primes.size() == 6 ); BOOST_ASSERT( primes.back() == 11 ); BOOST_ASSERT( primes.front() == 1 ); const stack<string> names = list_of( "Mr. Foo" )( "Mr. Bar")( "Mrs. FooBar" ).to_adapter(); const stack<string> names2 = (list_of( "Mr. Foo" ), "Mr. Bar", "Mrs. FooBar" ).to_adapter(); BOOST_ASSERT( names.size() == 3 ); BOOST_ASSERT( names.top() == "Mrs. FooBar" ); }
to_adapter()
. As the second example also shows,
we can use a comma-separated
list with list_of()
if we add parenthesis around the
entire right hand side. It is worth noticing that the first argument
of list_of()
determines the type of the anonymous list.
In case of the stack, the anonymous list consists of
const char*
objects which are then converted to
a stack of string
objects. The conversion is always
possible as long as the conversion between the stored types is possible.
Please notice that list_of()
can even convert to a
boost::array<T,sz>
and see also the list
of supported libraries .
map_list_of()
The function#include <boost/assign/list_of.hpp> // for 'map_list_of()' #include <boost/assert.hpp> #include <map> using namespace std; using namespace boost::assign; // bring 'map_list_of()' into scope { map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6); BOOST_ASSERT( next.size() == 5 ); BOOST_ASSERT( next[ 1 ] == 2 ); BOOST_ASSERT( next[ 5 ] == 6 ); // or we can use 'list_of()' by specifying what type // the list consists of next = list_of< pair<int,int> >(6,7)(7,8)(8,9); BOOST_ASSERT( next.size() == 3 ); BOOST_ASSERT( next[ 6 ] == 7 ); BOOST_ASSERT( next[ 8 ] == 9 ); }
pair_list_of()
may also be used.
tuple_list_of()
tuple_list_of()
:
#include <boost/assign/list_of.hpp> #include <vector> using namespace std; using namespace boost::assign; { typedef boost::tuple<int,std::string,int> tuple; vector<tuple> v = tuple_list_of( 1, "foo", 2 )( 3, "bar", 4 ); BOOST_CHECK( v.size() == 2 ); BOOST_CHECK( boost::get<0>( v[1] ) == 3 ); }
repeat()
and repeat_fun()
Sometimes it is too irritating to repeat the same value many times. This is
where repeat()
can be handy:
As we can see, then the first argument to#include <boost/assign/list_of.hpp> #include <boost/assign/std/vector.hpp> #include <boost/assert.hpp> using namespace std; using namespace boost::assign; { vector<int> v; v += 1,2,3,repeat(10,4),5,6,7,8,9; // v = [1,2,3,4,4,4,4,4,4,4,4,4,4,5,6,7,8,9] BOOST_ASSERT( v.size() == 3 + 10 + 5 ); v = list_of(1).repeat(5,2)(3); // v = [1,2,2,2,2,2,3] BOOST_ASSERT( v.size() == 1 + 5 + 1 ); push_back( v )(1).repeat(1,2)(3); // v = old v + [1,2,3] BOOST_ASSERT( v.size() == 10 ); }
repeat()
is the number
of times to repeat the second argument.
A more general list can be constructed with repeat_fun()
:
The only requirement of the second argument to#include <boost/assign/std/vector.hpp> #include <boost/assert.hpp> #include <cstdlib> // for 'rand()' using namespace std; using namespace boost::assign; template< class T > struct next { T seed; next( T seed ) : seed(seed) { } T operator()() { return seed++; } }; { vector<int> v; v += 1,2,repeat_fun(4,&rand),4; // v = [1,2,?,?,?,?,4] BOOST_ASSERT( v.size() == 7 ); push_back( v ).repeat_fun(4,next<int>(0))(4).repeat_fun(4,next<int>(5)); // v = old v + [0,1,2,3,4,5,6,7,8] BOOST_ASSERT( v.size() == 16 ); }
repeat_fun()
is that
it is a nullary function.
ref_list_of()
and cref_list_of()
You can only use lvalues with#include <boost/assign/list_of.hpp> #include <algorithm> // // Define Range algorithm // template< class Range > typename Range::const_iterator max_element( const Range& r ) { return std::max_element( r.begin(), r.end() ); } using namespace boost::assign; { int a=1,b=5,c=3,d=4,e=2,f=9,g=0,h=7; int& max = *max_element( ref_list_of<8>(a)(b)(c)(d)(e)(f)(g)(h) ); BOOST_CHECK_EQUAL( max, f ); max = 8; BOOST_CHECK_EQUAL( f, 8 ); const int& const_max = *max_element(cref_list_of<8>(a)(b)(c)(d)(e)(f)(g)(h) ); BOOST_CHECK_EQUAL( max, const_max ); }
ref_list_of()
while
cref_list_of()
accepts rvalues too. Do not worry about not
specifying exactly the right size; the extra space used is minimal and there
is no runtime overhead associated with it.
You may also use these functions instead of list_of()
if speed is
essential.
As a last example, let us assume that we need to keep track of the result of soccer matches. A team will get one point if it wins and zero otherwise. If there has been played three games in each group, the code might look like this:
In the first example, notice how the result of#include <boost/assign/list_of.hpp> #include <boost/assign/list_inserter.hpp> #include <boost/assert.hpp> #include <string> #include <vector> using namespace std; using namespace boost::assign; { typedef vector<int> score_type; typedef map<string,score_type> team_score_map; typedef pair<string,score_type> score_pair; team_score_map group1, group2; // // method 1: using 'insert()' // insert( group1 )( "Denmark", list_of(1)(1) ) ( "Germany", list_of(0)(0) ) ( "England", list_of(0)(1) ); BOOST_ASSERT( group1.size() == 3 ); BOOST_ASSERT( group1[ "Denmark" ][1] == 1 ); BOOST_ASSERT( group1[ "Germany" ][0] == 0 ); // // method 2: using 'list_of()' // group2 = list_of< score_pair > ( "Norway", list_of(1)(0) ) ( "USA", list_of(0)(0) ) ( "Andorra", list_of(1)(1) ); BOOST_ASSERT( group2.size() == 3 ); BOOST_ASSERT( group2[ "Norway" ][0] == 1 ); BOOST_ASSERT( group2[ "USA" ][0] == 0 ); }
list_of()
can be converted automatically to a vector<int>
because
insert()
knows it expects a vector<int>
.
In the second example we can see that list_of()
is somewhat
less intelligent since here it needs to be told explicitly what arguments to
expect. (In the future it might be possible to introduce a more intelligent
conversion layer in list_of()
.)
ptr_push_back(),
ptr_push_front()
and ptr_insert()
new
manually:
#include <boost/assign/ptr_list_inserter.hpp> #include <boost/ptr_container/ptr_deque.hpp> #include <boost/ptr_container/ptr_set.hpp> // // Example class // struct Foo { int i; Foo() : i(0) { } Foo( int i ) : i(i) { } Foo( int i, int ) : i(i) { } Foo( const char*, int i, int ) : i(i) { } }; // // Required by ptr_set<Foo> // inline bool operator<( Foo l, Foo r ) { return l.i < r.i; } using namespace boost; using namespace boost::assign; { ptr_deque<Foo> deq; ptr_push_back( deq )()(); BOOST_CHECK( deq.size() == 2u ); ptr_push_front( deq )( 3 )( 42, 42 )( "foo", 42, 42 ); BOOST_CHECK( deq.size() == 5 ); ptr_set<Foo> a_set; ptr_insert( a_set )()( 1 )( 2, 2 )( "foo", 3, 3 ); BOOST_CHECK( a_set.size() == 4 ); ptr_insert( a_set )()()()(); BOOST_CHECK( a_set.size() == 4 ); // duplicates not inserted }
ptr_list_of()
list_of()
to initialize containers, you can
use ptr_list_of()
to initialize a pointer container.
Here is a small example:
Notice the trailing#include <boost/assign/ptr_list_of.hpp> #include <boost/ptr_container/ptr_deque.hpp> using namespace boost; using namespace boost::assign; { ptr_deque<Foo> deq; deq = ptr_list_of<Foo>( 42 )()()( 3, 3 )( "foo", 2, 1 ).to_container( deq ); BOOST_CHECK( deq.size() == 5 ); }
.to_container(deq)
which helps many poor
compilers to figure out the conversion (a few get it right).
Notice also that pointer maps are
not supported.
That is all; now you are ready to use this library.
It is worth noticing the way the library is implemented.
A free-standing function (eg. push_back()
or operator+=()
) returns a proxy
object which is responsible for the insertion or the assignment. The proxy
object does the insertion or assignment by overloading operator,()
and operator()()
and by calling the "insert" function from within
those operators. The "insert" function is typically stored in the proxy object
by using boost::function
.
Often overloading
of operator,()
is discouraged because it can lead to surprising
results, but the approach taken in this library is safe since the
user never deals with objects that have overloaded operator,()
directly. However, you should be aware of this:
The expressions in a comma-separated list no longer follow the rules of the built-in comma-operator. This means that the order of evaluation of expressions in a comma-separated list is undefined like when one specifies a list of function arguments.
Most of the code in this document use int
in the examples,
but of course it works for arbitrary types as long as they are
Copy Constructible. The inserted data need not be constant data,
but can be variables or data returned from functions; the only requirement
is that the type of the data is convertible to the type stored in the
container.
All forwarding is done by passing objects by const
reference.
Originally arguments were passed by value (and still is in
tuple_list_of()
). One thing to remember is that references
can be passed by using boost::ref
.
Everything is put in namespace
boost::assign
.
More details can be found below:
list_of()
and map_list_of()
repeat()
and repeat_fun()
list_inserter
make_list_inserter()
An overview of the headers in this library
is given below. Please notice <boost/assign/list_inserter.hpp>
is included for each header that defines operator+=()
.
Header | Includes |
---|---|
<boost/assign.hpp> | everything except support for pointer containers |
<boost/assign/list_of.hpp> | list_of() , map_list_of(),
tuple_list_of(),
ref_list_of() and
cref_list_of()
|
<boost/assign/std.hpp> | operator+=() for all
standard
containers (see below) |
<boost/assign/std/deque.hpp> | operator+=() for
std::deque , <deque>
|
<boost/assign/std/list.hpp> | operator+=() for
std::list , <list>
|
<boost/assign/std/map.hpp> | operator+=() for
std::map and std::multimap ,
<map> |
<boost/assign/std/queue.hpp> | operator+=() for
std::queue and std::priority_queue ,
<queue> |
<boost/assign/std/set.hpp> | operator+=() for
std::set and std::multiset ,
<set> |
<boost/assign/std/slist.hpp> | operator+=() for
std::slist if the class is available ,
<slist> |
<boost/assign/std/stack.hpp> | operator+=() for
std::stack , <stack>
|
<boost/assign/std/vector.hpp> | operator+=() for
std::vector , <vector>
|
<boost/assign/assignment_exception.hpp> | Class assignment_exception which might
be thrown by the proxy returned by list_of()
|
<boost/assign/list_inserter.hpp> | Functions make_list_inserter() , push_back() ,
push_front() ,insert() ,
push() and class list_inserter
which is the back-bone of this entire library.
|
<boost/assign/ptr_list_inserter.hpp> | Functions ptr_push_back() ,
ptr_push_front() and ptr_insert()
|
<boost/assign/ptr_list_of.hpp> | Function ptr_list_of()
|
In the following three dots (...) will mean
implementation defined.
operator+=()
returns a proxy that forwards calls to either
push_back()
,insert()
, or push()
depending on which operation the container supports.
Note that the extra template argumentnamespace boost { namespace assign { template< class V, class A, class V2 > list_inserter< ... > operator+=( std::deque<V,A>& c, V2 v ); template< class V, class A, class V2 > list_inserter< ... > operator+=( std::list<V,A>& c, V2 v ); template< class K, class V, class C, class A, class P > list_inserter< ... > operator+=( std::map<K,V,C,A>& m, const P& p ); template< class K, class V, class C, class A, class P > list_inserter< ... > operator+=( std::multimap<K,V,C,A>& m, const P& p ); template< class V, class C, class V2 > list_inserter< ... > operator+=( std::queue<V,C>& c, V2 v ); template< class V, class C, class V2 > list_inserter< ... > operator+=( std::priority_queue<V,C>& c, V2 v ); template< class K, class C, class A, class K2 > list_inserter< ... > operator+=( std::set<K,C,A>& c, K2 k ); template< class K, class C, class A, class K2 > list_inserter< ... > operator+=( std::multiset<K,C,A>& c, K2 k ); #ifdef BOOST_HAS_SLIST template< class V, class A, class V2 > list_inserter< ... > operator+=( std::slist<V,A>& c, V2 v ); #endif template< class V, class C, class V2 > list_inserter< ... > operator+=( std::stack<V,C>& c, V2 v ); template< class V, class A, class V2 > list_inserter< ... > operator+=( std::vector<V,A>& c, V2 v ); } // namespace 'assign' } // namespace 'boost'
V2
etc. is
necessary to allow for types convertible to V
.
list_of()
and
map_list_of()
These two functions are used to construct anonymous
list which can be converted to any standard container
and boost::array<T,sz>.
The object returned by the two
functions is guaranteed to have the interface described below.
namespace boost { namespace assign { template< class T > class Implementation-defined { public: const_iterator begin() const; const_iterator end() const; template< class U > Implementation-defined& operator,( U u ); // inserts default-constructed object Implementation-defined& operator()(); template< class U > Implementation-defined& operator()( U u ); template< class U, class U2 > Implementation-defined& operator()( U u, U2 u2 ); // // and similarly up to 5 arguments // // // Convert to a 'Container'. 'Container' must have a constructor // which takes two iterators. // template< class Container > operator Container() const; // // Convert to a container adapter like 'std::stack<>'. // Convertible-to-adapter to_adapter() const; // // // Convert to eg. 'boost::array<T,std::size_t>'. If the // assigned variable is too small, // a assignment_exception is thrown. // If the assigned variable it is too big, the rest of the // values are default-constructed. // template< template <class,std::size_t> class Array, class U, std::size_t sz > operator Array<U,sz>() const; }; template< class T > Implementation-defined list_of(); template< class T > Implementation-defined list_of( T t ); template< class T, class U, class U2 > Implementation-defined list_of( U u, U2 u2 ); template< class T, class U, class U2, class U3 > Implementation-defined list_of( U u, U2 u2, U3 u3 ); template< class T, class U, class U2, class U3, class U4 > Implementation-defined list_of( U u, U2 u2, U3 u3, U4 u4 ); template< class T, class U, class U2, class U3, class U4, class U5 > Implementation-defined list_of( U u, U2 u2, U3 u3, U4 u4, U5 u5 ); template< class Key, class T > Implementation-defined map_list_of( Key k, T t ) { return list_of< std::pair<Key,T> >()( k, t ); } } // namespace 'assign' } // namespace 'boost'
repeat()
and
repeat_fun()
These two function exist both as free-standing functions and as member functions of the object returned by
list_of()
and of list_inserter
. The free-standing versions are used to create a
hook for operator,()
so we can call the functions in the middle of a comma-list. The member functions
are used when we need to call the functions in the middle of a parenthesis-list. In both cases we have that
repeat()
is (std::size_t,T)
, and
repeat_fun()
is (std::size_t,Nullary_function)
list_inserter
Synopsis
namespace boost { namespace assign { template< Function, Argument = void > class list_inserter { Function fun; public: explicit list_inserter( Function fun ); // conversion constructor template< class Function2, class Arg > list_inserter( const list_inserter<Function2,Arg>& ); public: template< class U > list_inserter& operator,( U u ); template< class U > list_inserter& operator=( U u ); // calls 'fun()' with default-constructed object list_inserter& operator()(); template< class U > list_inserter& operator()( U u ); template< class U, class U2 > list_inserter& operator()( U u, U2 u2 ) { // // if 'Argument' is 'void' // fun( u, u2 ); // else // fun( Argument( u, u2 ) ); // return *this; } // // similarly up to 5 arguments // }; template< class C > list_inserter< ... > push_back( C& ); template< class C > list_inserter< ... > push_front( C& ); template< class C > list_inserter< ... > insert( C& ); template< class C > list_inserter< ... > push( C& ); } // namespace 'assign' } // namespace 'boost'
Notice how the arguments to operator,()
and
operator()()
are passed differently to
fun
depending of the type of Argument
.
So if we only pass one template argument to list_inserter,
we can forward "arbitrary" argument lists of functions. If we pass
two template arguments to list_inserter
we can
construct types with "arbitrary" constructors.
And because
a reference to list_inserter
is returned, we can
chain argument list together in a very space-efficient manner.
make_list_inserter()
A simple "constructor" function for list_inserter
. A typical
use of this function is to call it with the result of
boost::bind()
which in general returns some unreadable and weird class template.
namespace boost { namespace assign { template< class Function > list_inserter<Function> make_list_inserter( Function fun ) { return list_inserter<Function>( fun ); } } }
This library uses the boost Preprocessor Library to implement overloaded
versions of operator()()
and list_of()
. By default you
can call these functions with five arguments, but you can also customize this
number by defining a macros before including a header from this library:
#define BOOST_ASSIGN_MAX_PARAMS 10 #include <boost/assign.hpp>
The exception guarantees by the library is the same as guarantee as the guarantee of the function that is forwarded to. For standard containers this means that the strong guarantee is given for a single insertions and that the basic guarantee is given for many insertions (provided that the object being copied gives the basic guarantee).
The functions may throw standard exceptions
like std::bad_alloc
. Note however that, unfortunately, the standard does not guarantee allocation-failures
in standard containers to be reported by std::bad_alloc
or exceptions derived from std::exception
.
assignment_exception
The exception is thrown by the conversion operator in the proxy object
returned from list_of()
.
namespace boost { namespace assign { class assignment_exception : public std::exception { public: explicit assignment_exception( const char* what ); virtual const char* what() const throw(); }; } }
It is very simple to make the library work with new classes.
This code shows how to use operator+=()
with
a container:
wheretemplate< class V, class A, class V2 > inline list_inserter< assign_detail::call_push_back< std::vector<V,A> >, V > operator+=( std::vector<V,A>& c, V2 v ) { return make_list_inserter( assign_detail::call_push_back< std::vector<V,A> >( c ) )( v ); }
call_push_back
is defined as
Note that we pass a second template argument totemplate< class C > class call_push_back { C& c_; public: call_push_back( C& c ) : c_( c ) { } template< class T > void operator()( T r ) { c_.push_back( r ); } };
list_inserter
so argument
lists will be used to construct a V
object. Otherwise we
could end up trying to call push_back()
with n arguments
instead of one.
An alternative way would be to use boost::function
and
boost::bind()
in combination. However, in this case one must
remember that it is illegal to take the address of a function in
the standard library.
Calling a function with more that one argument can be very useful too. This small example shows how we take advantage of this functionality:
The full example can be seen in email_example.cpp// // A class representing emails // class email { public: enum address_option { check_addr_book, dont_check_addr_book }; private: typedef std::map< std::string,address_option > address_map; // // Store list of persons that must be cc'ed // mutable address_map cc_list; // // This extra function-object will take care of the // insertion for us. It stores a reference to a // map and 'operator()()' does the work. // struct add_to_map { address_map& m; add_to_map( address_map& m ) : m(m) {} void operator()( const std::string& name, address_option ao ) { m[ name ] = ao; } }; public: // // This function constructs the appropriate 'list_inserter'. // Again we could have use 'boost::function', but it is // trivial to use a function object. // // Notice that we do not specify an extra template // parameter to 'list_inserter'; this means we forward // all parameters directly to the function without // calling any constructor. // list_inserter< add_to_map > add_cc( std::string name, address_option ao ) { // // Notice how we pass the arguments 'name' and 'ao' to // the 'list_inserter'. // return make_list_inserter( add_to_map( cc_list ) )( name, ao ); } }; // // Now we can use the class like this: // email e; e.add_cc( "Mr. Foo", email::dont_check_addr_book ) ( "Mr. Bar", email::check_addr_book ) ( "Mrs. FooBar", email::check_addr_book );
Additional examples can be found in the test files:
boost::array
boost::multi_index_container
Boost.Pointer Container
Library has been successfully compiled and tested with MVC++ 7.1, GCC 3.2 (under Cygwin) Comeau 4.3.3
There are known limitation on platforms not supporting templated
conversion operators. The solution is to call certain member functions on
the object returned by list_of()
:
{ using namespace std; using namespace boost; using namespace boost::assign; vector<int> v = list_of(1)(2)(3)(4).to_container( v ); set<int> s = list_of(1)(2)(3)(4).to_container( s ); map<int,int> m = map_list_of(1,2)(2,3).to_container( m ); stack<int> st = list_of(1)(2)(3)(4).to_adapter( st ); queue<int> q = list_of(1)(2)(3)(4).to_adapter( q ); array<int,4> a = list_of(1)(2)(3)(4).to_array( a ); }
Notice how one must supply the functions with an argument so the right return type can be deduced.
Some standard libraries are also broken. One problem is that
insert()
might not work:
The solution is to usemap<int,int> next; insert( next )(1,2)(2,3); // compile-time error
map_list_of()
instead:
map<int,int> next = map_list_of(1,2)(2,3);
The idea for an assignment/initialization library is not new. The functionality of this library resembles Leor Zolman's STL Container Initialization Library a great deal, but it does not rely on string parsing to achieve its goals.
The
library is non-intrusive and puts only a minimum of requirements
on its supported classes.
Overloading operator comma is sometimes viewed as a bad practice [1]. However, it has been done
with success in eg. the Generative Matrix Computation Library and Blitz to initialize matrices
(see [2]) and [3]). The
Initialization Library overloads
the comma operator in a safe manner by letting free standing functions
return an object that is responsible for the initialization. Therefore it takes
explicit
action from the programmer to begin using the overloaded operator,()
.
There has recently been some discussion about enhancing the language to support better initialization (see [4]).
Special thanks goes to
(C) Copyright Thorsten Ottosen 2003-2004