Parameters by value and by reference

Overview

In a normal call, assigning a new number to a parameter does not replace the caller’s numeric variable. With @ at the call site, the function can update that variable by reference. Arguments are positional rather than matched by local names. This example uses only a scalar to isolate the distinction. Arrays and objects need additional shared-content analysis; passing a container does not independently copy every element. (Sources: refs. 1–2.)

Syntax

Helper(nValue); Helper(@nValue)

Commented example

#Include "Protheus.ch"

User Function Ed570()
    Local nValue := 10
    // Only the second call can update the caller variable.
    IncrementValue(nValue)
    ConOut(cValToChar(nValue))
    IncrementValue(@nValue)
    ConOut(cValToChar(nValue))
Return Nil

Static Function IncrementValue(nValue)
    nValue := nValue + 1
Return nValue

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