If you consider the following function:

func MyFunc:
    inputs:
        myInput string (1..1)
        [metadata reference]
    output:
        myResult string (1..1)

    set myResult: myInput -> reference

In the above example the scheme of the input is not preserved on the way into the function so this will result in an error in the generated code.

Additionally the following example:

func MyFunc2:
    inputs:
        myInput string (1..*)
        [metadata reference]
    output:
        myResult string (1..*)
    set myResult: myInput extract reference

In this example you currently get a syntax error as the metadata is lost prior to using the extract operator.

This issue proposes that we support the concept of passing metadata to function and between expression operators and in doing so support the above two examples.

An additional aspect of this change will be to support checking of the meta types when passing between functions and expressions. So if you consider the following:

func MyFunc3:
    inputs:
        myInput string (1..1)
    output:
        myResult string (1..1)
    set myResult: MyFunc(myInput)

This above set operation will now be invalid as MyFunc requires a string with a metadata reference but instead got just a string.