rego::Output Class Reference

Encapsulates the output of a Rego query. More...

#include <rego.hh>

Public Member Functions
	Output (Node node)
	Constructor.
bool	ok () const
	Whether the Output is OK (i.e., has not resulted in one or more errors)
Node	node () const
	Gets the underlying node.
size_t	size () const
	Gets the number of results.
Node	expressions_at (size_t index) const
	Gets the expressions for the result at the specified index.
Node	expressions () const
	Gets the expressions for the first result.
Node	binding_at (size_t index, const std::string &name) const
	Gets the binding for the specified name at the specified result index.
Node	binding (const std::string &name) const
	Gets the binding for the specified name at the first result.
const std::string &	json () const
	Gets the JSON representation of the output.
std::vector< std::string >	errors () const
	Gets the errors in the output.

Detailed Description

Encapsulates the output of a Rego query.

The Output class encapsulates the output of a Rego query. A Rego query result can be either undefined (no results), one or more errors, or one or more results. The fact that a query can result in one or more results may seem surprising. The query a = [1, 2, 3, 4]; x = a[_]; x % 2 == 0; x / 2 results in two distinct solutions:

{"expressions":[true, true, true, 1], "bindings":{"a":[1,2,3,4], "x":2}}
{"expressions":[true, true, true, 2], "bindings":{"a":[1,2,3,4], "x":4}}

Each result consists of a list of expressions (one for each statement in the query) and a lookup table of bindings, with assigned values for each named local. This class provides methods for accessing these value. Using the output above:

rego::Node expressions0 = output.expressions();
rego::Node expressions1 = output.expressions_at(1);
rego::Node last0 = expressions0->back();
std::cout << rego::to_key(last0);
// 1
rego::Node last1 = expressions1->back();
std::cout << rego::to_key(last1);
// 2
Node a = output.binding("a");
std::cout << rego::to_key(a);
// [1,2,3,4]
auto x0 = rego::get_int(output.binding("x"));
std::cout << x0;
// 2
auto x1 = rego::get_int(output.binding_at(1, "x"));
std::cout << x1;
// 4

Constructor & Destructor Documentation

Output()

rego::Output::Output

(

Node

node

)

Constructor.

Parameters

node	A Results or ErrorSeq node.

Member Function Documentation

binding()

Node rego::Output::binding

(

const std::string &

name

)

const

Gets the binding for the specified name at the first result.

Parameters

name	The name of the binding.

Returns

The binding for the specified name.

binding_at()

Node rego::Output::binding_at	(	size_t	index,
		const std::string &	name
	)		const

Gets the binding for the specified name at the specified result index.

Parameters

index	The index of the result.
name	The name of the binding.

Returns

The binding for the specified name.

errors()

std::vector< std::string > rego::Output::errors

(

)

const

Gets the errors in the output.

If the output is not OK, this method can be used to retrieve the error messages.

Returns

The errors in the output.

expressions()

Node rego::Output::expressions

(

)

const

Gets the expressions for the first result.

Returns

The expressions for the first result.

expressions_at()

Node rego::Output::expressions_at

(

size_t

index

)

const

Gets the expressions for the result at the specified index.

Parameters

index

The index of the result.

Returns

The expressions for the result.

json()

const std::string & rego::Output::json

(

)

const

Gets the JSON representation of the output.

Returns

The JSON representation of the output.

node()

Node rego::Output::node

(

)

const

Gets the underlying node.

Returns

The underlying node.

ok()

bool rego::Output::ok

(

)

const

Whether the Output is OK (i.e., has not resulted in one or more errors)

Returns

True if the Output is OK, otherwise false.

size()

size_t rego::Output::size

(

)

const

Gets the number of results.

There will be one result per solution to the query.

Returns

The number of results.

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The documentation for this class was generated from the following file:

• include/rego/rego.hh