...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Generator sequences are used to consecutively combine different, more primitive generators. All generators in a sequence are invoked from left to right as long as they succeed.
// forwards to <boost/spirit/home/karma/operator/sequence.hpp> #include <boost/spirit/include/karma_sequence.hpp>
Also, see Include Structure.
Semantics of an expression is defined only where it differs from, or
is not defined in NaryGenerator
.
Expression |
Semantics |
---|---|
|
The generators |
It is important to note, that sequences don't perform any buffering of the output generated by its elements. That means that any failing sequence might have already generated some output, which is not rolled back.
Tip | |
---|---|
The simplest way to force a sequence to behave as if it did buffering
is to wrap it into a buffering directive (see
buffer[a << b << c]
which will not generate any output in case of a failing sequence. |
See Compound Attribute Notation.
Expression |
Attribute |
---|---|
|
a: A, b: B --> (a << b): tuple<A, B> a: A, b: Unused --> (a << b): A a: Unused, b: B --> (a << b): B a: Unused, b: Unused --> (a << b): Unused a: A, b: A --> (a << b): vector<A> a: vector<A>, b: A --> (a << b): vector<A> a: A, b: vector<A> --> (a << b): vector<A> a: vector<A>, b: vector<A> --> (a << b): vector<A>
|
Important | |
---|---|
The table above uses
The notation
The notation of |
The attribute composition and propagation rules as shown in the table above make sequences somewhat special as they can operate in two modes if all elements have the same attribute type: consuming fusion sequences and consuming STL containers. The selected mode depends on the type of the attribute supplied.
The overall complexity of the sequence generator is defined by the sum of the complexities of its elements. The complexity of the sequence itself is O(N), where N is the number of elements in the sequence.
Note | |
---|---|
The test harness for the example(s) below is presented in the Basics Examples section. |
Some includes:
#include <boost/spirit/include/karma.hpp> #include <boost/spirit/include/phoenix_core.hpp> #include <boost/spirit/include/phoenix_operator.hpp> #include <boost/fusion/include/std_pair.hpp> #include <iostream> #include <string>
Some using declarations:
using boost::spirit::karma::double_;
Basic usage of a sequence:
test_generator_attr("1.0,2.0", double_ << ',' << double_, std::make_pair(1.0, 2.0));