Can I get ExtraDiskSpaceRequired from code?

[George Hovhannisian]

This is what I'm trying to do:

[Setup]

ExtraDiskSpaceRequired={code:GetRequiredDiscSpace}

[Code]

function GetRequiredDiscSpace(Param: String): String;
begin
  Result := '1234';
end;

However the compiler says that the value is invalid.

[Gavin Lambert]

Unless the documentation for a [Setup] setting explicitly says "The
value may include constants", it can't. This is generally limited to
string values only used at runtime.

As far as I am aware, the only way to programmatically manipulate this
value is to select/deselect components (using either their real sizes or
the ExtraDiskSpaceRequired value at the component level, which also
cannot include constants).

Bear in mind that the disk space usage is cited as a minimum, and as
such is basically useless anyway.