Platform-specific support

The VA Smalltalk DDE subsystem was developed as an extension to the DDE support provided by Microsoft Windows. The following figure illustrates the layers provided by the VA Smalltalk Base DDE subsystem.

The application programmer can skip the provided VA Smalltalk DDE layer and program directly to the operating system support mechanisms in the platform interface layer.

In the platform interface layer, objects have been created for all C data types for Microsoft Windows. These data types include items such as DDEACK, DDEADVISE, DDEDATA, and HWND. These data objects are named by prefixing the data type name with OS, and applying bicapitalization rules. For example, HWND becomes OSHwnd. Additionally, each operating system C function has been converted to a corresponding Smalltalk method. To understand this conversion, consider the standard Windows function WinDdePostMsg:

WinDdePostMsg( hwndDest, hwndSource, msg, ddeStruct, 1)

This function has been converted to the following:

OSHwnd>>winDdePostMsg: hwndFrom wm: wm pddest:pddest

flOptions:flOptions

In translating C functions to Smalltalk, two rules have been applied:

•	If there is no Smalltalk object that corresponds to the first parameter, then the receiver of the message is OSCall. Otherwise, the receiver is the first parameter of the function.

•	The Smalltalk message selector is formed from the C function name and the remaining parameter names.