FHIRPath Function: defineVariable

{:.stu}

Note: The contents of this section are Standard for Trial Use (STU) {: .stu-note }

Defines a variable named name that is accessible in subsequent expressions on the output collection and has the value of projection if present, otherwise the value of the input collection. In either case the function does not change the input and the output is the same as the input collection. {:.stu}

Note: This is not a scoped function, it does not change any variables such as $this or $index.<br/>

This function is the only function that changes the state of the context for processing on the output collection.<br/> Whereas scoped functions only impact the context while evaluating the function, and it's parameters, and the context is restored to the same as before the function was called. {:.stu}

If the name already exists in the current expression scope, the evaluation will end and signal an error to the calling environment. {:.stu}

Example: {:.stu}

group.select(
  defineVariable('grp')
  .select(
    element.select(
      defineVariable('src')
      .target.select(
        %grp.source & '#' & %src.code
        & ' ' & equivalence & ' '
        & %grp.target & '#' & code
      )
    )
  )
)

{:.stu}

Note: this could be implemented using expression scoping on the variable stack and after expression completion the temporary variable would be popped off the stack. {:.stu}

Summary

• Category: Utility functions
• Section: 5.10.4
• Return Type: collection
• Empty Input Result: empty
• Errors on Multiple Input: false

Description

Defines a variable named name that is accessible in subsequent expressions and has the value of expr if present, otherwise the value of the input collection.

Arguments

• name: String - Name of the variable
• expr (optional): expression - Optional expression for the variable's value

Type Mapping

• Any-Any

Example

group.select(defineVariable('grp'))