The Slice Language

Slice (Specification Language for Ice) is the fundamental abstraction mechanism for separating object interfaces from their implementations. Slice establishes a contract between client and server that describes the interfaces, operations and parameter types used by an application. This description is independent of the implementation language, so it does not matter whether the client is written in the same language as the server.

Even though Slice is an acronym, it is pronounced as a single syllable, like a slice of bread.

Slice definitions are compiled for a particular implementation language by a compiler. The language-specific Slice compiler translates the language-independent Slice definitions into language-specific type definitions and APIs. These types and APIs are used by the developer to provide application functionality and to interact with Ice. The translation algorithms for various implementation languages are known as language mappings, and Ice provides a number of language mappings (for C++, C#, Java, JavaScript, Python and more).

Because Slice describes interfaces and types (but not implementations), it is a purely declarative language; there is no way to write executable statements in Slice.

Slice definitions focus on object interfaces, the operations supported by those interfaces, and exceptions that may be raised by operations. This requires quite a bit of supporting machinery; in particular, much of Slice is concerned with the definition of data types. This is because data can be exchanged between client and server only if their types are defined in Slice. You cannot exchange arbitrary C++ data between a client and a server because it would destroy the language independence of Ice. However, you can always create a Slice type definition that corresponds to the C++ data you want to send, and then you can transmit the Slice type.

We present the full syntax and semantics of Slice here. Because much of Slice is based on C++ and Java, we focus on those areas where Slice differs from C++ or Java or constrains the equivalent C++ or Java feature in some way. Slice features that are identical to C++ and Java are mentioned mostly by example.