Conversion Functions

Conversion functions allow you to convert values between FHIRPath types (Boolean, Integer, Decimal, String, Date, DateTime, Time, Quantity) and to test whether such conversions are possible. The iif function provides conditional evaluation.

Each to* function performs the actual conversion (returning empty if conversion fails), while its corresponding convertsTo* function returns a boolean indicating whether the conversion would succeed.

iif

Conditional function that returns one of two values depending on a boolean condition. This is the FHIRPath equivalent of a ternary operator.

Signature:

iif(condition : Boolean, trueResult : Expression [, falseResult : Expression]) : Collection

Parameters:

Return Type: Collection

Examples:

result, _ := fhirpath.Evaluate(patient, "iif(Patient.active, 'Active', 'Inactive')")
// Returns 'Active' if patient is active, 'Inactive' otherwise

result, _ := fhirpath.Evaluate(patient, "iif(Patient.birthDate.exists(), Patient.birthDate, 'Unknown')")
// Returns birth date if it exists, otherwise 'Unknown'

result, _ := fhirpath.Evaluate(patient, "iif(Patient.gender = 'male', 'M', 'F')")
// Returns 'M' or 'F' based on gender

Edge Cases / Notes:

• If the condition is empty or not a boolean, it is treated as false.
• If the falseResult is not provided and the condition is false, returns an empty collection.
• Both branches are evaluated as expressions and passed as collections.

toBoolean

Converts the input to a Boolean value.

Signature:

toBoolean() : Boolean

Return Type: Boolean

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "'true'.toBoolean()")
// true

result, _ := fhirpath.Evaluate(resource, "(1).toBoolean()")
// true

result, _ := fhirpath.Evaluate(resource, "'yes'.toBoolean()")
// true

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted (e.g., 'maybe'.toBoolean()).
• Returns empty collection if the input is empty.
• String comparison is case-insensitive.

convertsToBoolean

Returns true if the input can be converted to a Boolean using toBoolean().

Signature:

convertsToBoolean() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'true'.convertsToBoolean()")
// true

result, _ := fhirpath.Evaluate(resource, "'maybe'.convertsToBoolean()")
// false

result, _ := fhirpath.Evaluate(resource, "(1).convertsToBoolean()")
// true

Edge Cases / Notes:

• Returns false for empty input.
• Returns false for Integer values other than 0 and 1.

toInteger

Converts the input to an Integer value.

Signature:

toInteger() : Integer

Return Type: Integer

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "'42'.toInteger()")
// 42

result, _ := fhirpath.Evaluate(resource, "true.toInteger()")
// 1

result, _ := fhirpath.Evaluate(resource, "(3.7).toInteger()")
// 3

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted (e.g., 'abc'.toInteger()).
• Returns empty collection if the input is empty.
• For Decimal input, the fractional part is discarded (truncation toward zero).

convertsToInteger

Returns true if the input can be converted to an Integer using toInteger().

Signature:

convertsToInteger() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'42'.convertsToInteger()")
// true

result, _ := fhirpath.Evaluate(resource, "'3.14'.convertsToInteger()")
// false

result, _ := fhirpath.Evaluate(resource, "true.convertsToInteger()")
// true

Edge Cases / Notes:

• Returns false for empty input.
• Returns true for Decimal values (they can always be truncated).
• Returns false for strings that are not valid integers.

toDecimal

Converts the input to a Decimal value.

Signature:

toDecimal() : Decimal

Return Type: Decimal

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "'3.14'.toDecimal()")
// 3.14

result, _ := fhirpath.Evaluate(resource, "(42).toDecimal()")
// 42.0

result, _ := fhirpath.Evaluate(resource, "true.toDecimal()")
// 1.0

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted.
• Returns empty collection if the input is empty.
• Uses the shopspring/decimal library for precise decimal arithmetic.

convertsToDecimal

Returns true if the input can be converted to a Decimal using toDecimal().

Signature:

convertsToDecimal() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'3.14'.convertsToDecimal()")
// true

result, _ := fhirpath.Evaluate(resource, "'not-a-number'.convertsToDecimal()")
// false

result, _ := fhirpath.Evaluate(resource, "(42).convertsToDecimal()")
// true

Edge Cases / Notes:

• Returns false for empty input.
• Integer, Decimal, and Boolean always convert to Decimal.

toString

Converts the input to a String representation.

Signature:

toString() : String

Return Type: String

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "(42).toString()")
// '42'

result, _ := fhirpath.Evaluate(resource, "true.toString()")
// 'true'

result, _ := fhirpath.Evaluate(resource, "(3.14).toString()")
// '3.14'

Edge Cases / Notes:

• Returns empty collection if the input is empty.
• All primitive types can be converted to string using their .String() representation.

convertsToString

Returns true if the input can be converted to a String using toString().

Signature:

convertsToString() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "(42).convertsToString()")
// true

result, _ := fhirpath.Evaluate(resource, "true.convertsToString()")
// true

result, _ := fhirpath.Evaluate(resource, "'hello'.convertsToString()")
// true

Edge Cases / Notes:

• Returns false for empty input.
• Returns true for all primitive types (String, Boolean, Integer, Decimal).
• Returns false for complex types (objects).

toDate

Converts the input to a Date value.

Signature:

toDate() : Date

Return Type: Date

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "'2024-01-15'.toDate()")
// @2024-01-15

result, _ := fhirpath.Evaluate(patient, "Patient.birthDate.toDate()")
// Returns the birth date as a Date type

result, _ := fhirpath.Evaluate(resource, "'not-a-date'.toDate()")
// { } (empty - invalid date string)

Edge Cases / Notes:

• Returns empty collection if the input cannot be parsed as a date.
• Returns empty collection if the input is empty.
• For DateTime input, extracts the first 10 characters (the date portion).

convertsToDate

Returns true if the input can be converted to a Date using toDate().

Signature:

convertsToDate() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'2024-01-15'.convertsToDate()")
// true

result, _ := fhirpath.Evaluate(resource, "'not-a-date'.convertsToDate()")
// true (basic check -- returns true for any string)

result, _ := fhirpath.Evaluate(resource, "(42).convertsToDate()")
// false

Edge Cases / Notes:

• Returns false for empty input.
• The current implementation performs a basic type check (returns true for any string). This may be enhanced in future versions with stricter date format validation.

toDateTime

Converts the input to a DateTime value.

Signature:

toDateTime() : DateTime

Return Type: DateTime

Examples:

result, _ := fhirpath.Evaluate(resource, "'2024-01-15T10:30:00Z'.toDateTime()")
// @2024-01-15T10:30:00Z

result, _ := fhirpath.Evaluate(resource, "'2024-01-15'.toDateTime()")
// Converts date string to DateTime

result, _ := fhirpath.Evaluate(resource, "(42).toDateTime()")
// { } (empty - integer cannot convert to DateTime)

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted.
• Returns empty collection if the input is empty.
• Currently accepts String input for conversion.

convertsToDateTime

Returns true if the input can be converted to a DateTime using toDateTime().

Signature:

convertsToDateTime() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'2024-01-15T10:30:00Z'.convertsToDateTime()")
// true

result, _ := fhirpath.Evaluate(resource, "(42).convertsToDateTime()")
// false

Edge Cases / Notes:

• Returns false for empty input.
• Returns true for String input (basic type check).

toTime

Converts the input to a Time value.

Signature:

toTime() : Time

Return Type: Time

Examples:

result, _ := fhirpath.Evaluate(resource, "'14:30:00'.toTime()")
// @T14:30:00

result, _ := fhirpath.Evaluate(resource, "'10:00:00.000'.toTime()")
// @T10:00:00.000

result, _ := fhirpath.Evaluate(resource, "(42).toTime()")
// { } (empty - integer cannot convert to Time)

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted.
• Returns empty collection if the input is empty.
• Currently accepts String input for conversion.

convertsToTime

Returns true if the input can be converted to a Time using toTime().

Signature:

convertsToTime() : Boolean

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "'14:30:00'.convertsToTime()")
// true

result, _ := fhirpath.Evaluate(resource, "(42).convertsToTime()")
// false

Edge Cases / Notes:

• Returns false for empty input.
• Returns true for String input (basic type check).

toQuantity

Converts the input to a Quantity value, optionally with a specified unit.

Signature:

toQuantity([unit : String]) : Quantity

Parameters:

Return Type: Quantity

Conversion Rules:

Examples:

result, _ := fhirpath.Evaluate(resource, "(42).toQuantity('mg')")
// 42 'mg'

result, _ := fhirpath.Evaluate(resource, "'5.5 mg'.toQuantity()")
// 5.5 'mg' (parsed from string)

result, _ := fhirpath.Evaluate(resource, "(3.14).toQuantity()")
// 3.14 (unitless quantity)

Edge Cases / Notes:

• Returns empty collection if the input cannot be converted.
• Returns empty collection if the input is empty.
• String parsing supports UCUM unit notation.

convertsToQuantity

Returns true if the input can be converted to a Quantity using toQuantity(). Optionally checks if the quantity can be expressed in the specified unit.

Signature:

convertsToQuantity([unit : String]) : Boolean

Parameters:

Return Type: Boolean

Examples:

result, _ := fhirpath.Evaluate(resource, "(42).convertsToQuantity()")
// true

result, _ := fhirpath.Evaluate(resource, "'5.5 mg'.convertsToQuantity()")
// true

result, _ := fhirpath.Evaluate(resource, "'not-a-quantity'.convertsToQuantity()")
// false

Edge Cases / Notes:

• Returns false for empty input.
• Integer and Decimal always convert to Quantity.
• When a target unit is specified, checks UCUM unit compatibility between the source and target units using normalization.