Who should read this chapter

This chapter is for developers needing to interface to other languages or write custom primitive operations.

Some reasons to interface to other languages are:

•	Low-level operating system interface requirements

•	Performance-critical code or enhancements

•	Preserving existing business-critical code

You can use either of two mechanisms for interfacing to C code:

•	PlatformFunction

•	User primitives

If you need to interface to existing code written in C or other languages (operating system code, for example), you would use PlatformFunction, because it does not require you to write any C code. You can interface to C code using PlatformFunction completely from Smalltalk. PlatformFunction enables you to call arbitrary code that knows nothing about objects.

User primitives enable you to write performance-critical code that is Smalltalk-specific. This code is aware of Smalltalk objects. For this reason, these primitives can be very fast, and you can use them to improve performance.

This chapter assumes a familiarity with the C programming language and with the C compiler for the VA Smalltalk platform.