bcquality/custom/knowledge/style/var-parameters-require-an-addressable-variable.md

bc-version	domain	keywords	technologies	countries	application-area
all	style	var-parameter by-reference pass-by-reference literal constant compile-error procedure-call	al	w1	all

A var parameter must be called with a variable, never a literal or expression

Description

When a procedure declares a parameter with var — procedure DoSomething(var Result: Text) — that parameter is passed by reference: the callee writes back into the caller's own memory location. This means the argument at the call site must be an actual variable, something with an address. A string literal, a numeric constant, or a computed expression has no address to write back to, so passing one to a var parameter fails to compile.

This is a known failure mode when generating AL code without tracking which parameters on a called procedure are declared var: a call that would be valid for a by-value parameter (DoSomething('Hello'), DoSomething(SomeText + Suffix)) is invalid the moment that same parameter position is var. Before writing a call, check the callee's signature for var on each parameter position being supplied a literal or expression — if present, a variable declared in the caller's own scope must be used instead, even if that means declaring a throwaway local variable just to hold the value.

Best Practice

procedure GetCustomerName(CustomerNo: Code[20]; var Name: Text[100])
begin
    if Customer.Get(CustomerNo) then
        Name := Customer.Name;
end;

var
    CustName: Text[100];
...
GetCustomerName('10000', CustName);

Anti Pattern

procedure GetCustomerName(CustomerNo: Code[20]; var Name: Text[100])
begin
    if Customer.Get(CustomerNo) then
        Name := Customer.Name;
end;
...
GetCustomerName('10000', 'placeholder'); // compile error: cannot pass a literal to a var parameter
GetCustomerName('10000', CustName + ''); // compile error: an expression is not addressable either

Both anti-pattern calls fail to compile with an error to the effect of "a var parameter requires a variable" — the fix is always to declare (or reuse) a variable for that argument position, never to reach for a literal or expression because the value "looks" like what the parameter should receive.