**Library:** Foundation

**Package:** Dynamic

**Header:** Poco/Dynamic/Var.h

Var allows to store data of different types and to convert between these types transparently. Var puts forth the best effort to provide intuitive and reasonable conversion semantics and prevent unexpected data loss, particularly when performing narrowing or signedness conversions of numeric data types.

An attempt to convert or extract from a non-initialized (“empty”) Var variable shall result in an exception being thrown.

Loss of signedness is not allowed for numeric values. This means that if an attempt is made to convert the internal value which is a negative signed integer to an unsigned integer type storage, a RangeException is thrown. Overflow is not allowed, so if the internal value is a larger number than the target numeric type size can accomodate, a RangeException is thrown.

Precision loss, such as in conversion from floating-point types to integers or from double to float on platforms where they differ in size (provided internal actual value fits in float min/max range), is allowed.

String truncation is allowed — it is possible to convert between string and character when string length is greater than 1. An empty string gets converted to the char '\0', a non-empty string is truncated to the first character.

Boolean conversion is performed as follows:

A string value "false" (not case sensitive), "0" or "" (empty string) can be converted to a boolean value false, any other string not being false by the above criteria evaluates to true (e.g: "hi" -> true). Integer 0 values are false, everything else is true. Floating point values equal to the minimal FP representation on a given platform are false, everything else is true.

Arithmetic operations with POD types as well as between Var's are supported, subject to following limitations:

- for std::string and const char* values, only '+' and '+=' operations are supported

- for integral and floating point numeric values, following operations are supported:

'+', '+=', '-', '-=', '*', '*=' , '/' and '/='

- for integral values, following operations are supported:

prefix and postfix increment (++) and decement (--)

- for all other types, InvalidArgumentException is thrown upon attempt of an arithmetic operation

A Var can be created from and converted to a value of any type for which a specialization of VarHolderImpl is available. For supported types, see VarHolder documentation.

**Member Functions: **convert, empty, extract, isArray, isEmpty, isInteger, isNumeric, isSigned, isString, isStruct, operator !, operator !=, operator &&, operator *, operator *=, operator +, operator ++, operator +=, operator -, operator --, operator -=, operator /, operator /=, operator <, operator <=, operator =, operator ==, operator >, operator >=, operator T, operator [], operator ||, parse, swap, toString, type

Var();

Creates an empty Var.

template < typename T > Var(

const T & val

);

Creates the Var from the given value.

Var(

const char * pVal

);

Copy constructor.

~Var();

Destroys the Var.

template < typename T > void convert(

T & val

) const;

Invoke this method to perform a safe conversion.

Example usage:

Var any("42"); int i; any.convert(i);

Throws a RangeException if the value does not fit into the result variable. Throws a NotImplementedException if conversion is not available for the given type. Throws InvalidAccessException if Var is empty.

template < typename T > T convert() const;

Invoke this method to perform a safe conversion.

Example usage:

Var any("42"); int i = any.convert<int>();

Throws a RangeException if the value does not fit into the result variable. Throws a NotImplementedException if conversion is not available for the given type. Throws InvalidAccessException if Var is empty.

void empty();

Empties Var.

template < typename T > const T & extract() const;

Returns a const reference to the actual value.

Must be instantiated with the exact type of the stored value, otherwise a BadCastException is thrown. Throws InvalidAccessException if Var is empty.

bool isArray() const;

Returns true if Var represents a vector

bool isEmpty() const;

Returns true if empty.

bool isInteger() const;

Returns true if stored value is integer.

bool isNumeric() const;

Returns true if stored value is numeric. Returns false for numeric strings (e.g. "123" is string, not number)

bool isSigned() const;

Returns true if stored value is signed.

bool isString() const;

Returns true if stored value is std::string.

bool isStruct() const;

Returns true if Var represents a struct

bool operator ! () const;

Logical NOT operator.

template < typename T > bool operator != (

const T & other

) const;

Inequality operator

bool operator != (

const Var & other

) const;

Inequality operator overload for Var

bool operator != (

const char * other

) const;

Inequality operator overload for const char*

template < typename T > bool operator && (

const T & other

) const;

Logical AND operator

bool operator && (

const Var & other

) const;

Logical AND operator operator overload for Var

template < typename T > const Var operator * (

const T & other

) const;

Multiplication operator for multiplying Var with POD

const Var operator * (

const Var & other

) const;

Multiplication operator overload for Var

template < typename T > Var & operator *= (

const T & other

);

Multiplication asignment operator

Var & operator *= (

const Var & other

);

Multiplication asignment operator overload for Var

template < typename T > const Var operator + (

const T & other

) const;

Addition operator for adding POD to Var

const Var operator + (

const Var & other

) const;

Addition operator specialization for Var

const Var operator + (

const char * other

) const;

Addition operator specialization for adding const char* to Var

Var & operator ++ ();

Pre-increment operator

const Var operator ++ (

int

);

Post-increment operator

template < typename T > Var & operator += (

const T & other

);

Addition asignment operator for addition/assignment of POD to Var.

Var & operator += (

const Var & other

);

Addition asignment operator overload for Var

Var & operator += (

const char * other

);

Addition asignment operator overload for const char*

template < typename T > const Var operator - (

const T & other

) const;

Subtraction operator for subtracting POD from Var

const Var operator - (

const Var & other

) const;

Subtraction operator overload for Var

Var & operator -- ();

Pre-decrement operator

const Var operator -- (

int

);

Post-decrement operator

template < typename T > Var & operator -= (

const T & other

);

Subtraction asignment operator

Var & operator -= (

const Var & other

);

Subtraction asignment operator overload for Var

template < typename T > const Var operator / (

const T & other

) const;

Division operator for dividing Var with POD

const Var operator / (

const Var & other

) const;

Division operator overload for Var

template < typename T > Var & operator /= (

const T & other

);

Division asignment operator

Var & operator /= (

const Var & other

);

Division asignment operator specialization for Var

template < typename T > bool operator < (

const T & other

) const;

Less than operator

bool operator < (

const Var & other

) const;

Less than operator overload for Var

template < typename T > bool operator <= (

const T & other

) const;

Less than or equal operator

bool operator <= (

const Var & other

) const;

Less than or equal operator overload for Var

template < typename T > Var & operator = (

const T & other

);

Assignment operator for assigning POD to Var

Var & operator = (

const Var & other

);

Assignment operator specialization for Var

template < typename T > bool operator == (

const T & other

) const;

Equality operator

bool operator == (

const char * other

) const;

Equality operator overload for const char*

bool operator == (

const Var & other

) const;

Equality operator overload for Var

template < typename T > bool operator > (

const T & other

) const;

Greater than operator

bool operator > (

const Var & other

) const;

Greater than operator overload for Var

template < typename T > bool operator >= (

const T & other

) const;

Greater than or equal operator

bool operator >= (

const Var & other

) const;

Greater than or equal operator overload for Var

template < typename T > operator T() const;

Safe conversion operator for implicit type conversions. If the requested type T is same as the type being held, the operation performed is direct extraction, otherwise it is the conversion of the value from type currently held to the one requested.

Throws a RangeException if the value does not fit into the result variable. Throws a NotImplementedException if conversion is not available for the given type. Throws InvalidAccessException if Var is empty.

template < typename T > Var & operator[] (

T n

);

Index operator, only use on Vars where isArray() or isStruct() returns true! In all other cases InvalidAccessException is thrown.

template < typename T > const Var & operator[] (

T n

) const;

const Index operator, only use on Vars where isArray() or isStruct() returns true! In all other cases InvalidAccessException is thrown.

Var & operator[] (

const std::string & name

);

Index operator by name, only use on Vars where isStruct returns true! In all other cases InvalidAccessException is thrown.

const Var & operator[] (

const std::string & name

) const;

Var & operator[] (

const char * name

);

const Var & operator[] (

const char * name

) const;

template < typename T > bool operator || (

const T & other

) const;

Logical OR operator

bool operator || (

const Var & other

) const;

Logical OR operator operator overload for Var

static Var parse(

const std::string & val

);

Parses the string which must be in JSON format

void swap(

Var & other

);

static std::string toString(

const Var & any

);

Converts the Var to a string in JSON format. Note that toString will return a different result than any.convert<std::string>()!

const std::type_info & type() const;

Returns the type information of the stored content.