Slice Source Files

Slice defines a number of rules for the naming and contents of Slice source files.

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File Naming

Files containing Slice definitions must end in a .ice file extension, for example, Clock.ice is a valid file name. Other file extensions are rejected by the compilers.

For case-insensitive file systems, the file extension may be written as uppercase or lowercase, so Clock.ICE is legal. For case-sensitive file systems (such as Unix), Clock.ICE is illegal. (The extension must be in lowercase.)

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File Format

Slice is a free-form language so you can use spaces, horizontal and vertical tab stops, form feeds, and newline characters to lay out your code in any way you wish. (White space characters are token separators). Slice does not attach semantics to the layout of a definition. You may wish to follow the style we have used for the Slice examples throughout this book.

Slice files can be ASCII text files or use the UTF-8 character encoding with an optional byte order marker (BOM) at the beginning of each file. However, Slice identifiers are limited to ASCII letters and digits; non-ASCII letters can appear only in comments and string literals.

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Preprocessing

Slice supports the same preprocessor directives as C++, so you can use directives such as #include and macro definitions. However, Slice permits #include directives only at the beginning of a file, before any Slice definitions.

If you use #include directives, it is a good idea to protect them with guards to prevent double inclusion of a file:

Slice
// File Clock.ice
#ifndef _CLOCK_ICE
#define _CLOCK_ICE

// #include directives here...
// Definitions here...

#endif _CLOCK_ICE

The following #pragma directive offers a simpler way to achieve the same result:

Slice
// File Clock.ice
#pragma once

// #include directives here...
// Definitions here...

#include directives permit a Slice definition to use types defined in a different source file. The Slice compilers parse all of the code in a source file, including the code in subordinate #include files. However, the compilers generate code only for the top-level file(s) nominated on the command line. You must separately compile subordinate #include files to obtain generated code for all the files that make up your Slice definition.

Note that you should avoid #include with double quotes:

Slice
#include "Clock.ice" // Not recommended!

While double quotes will work, the directory in which the preprocessor tries to locate the file can vary depending on the operating system, so the included file may not always be found where you expect it. Instead, use angle brackets (<>); you can control which directories are searched for the file with the -I option of the Slice compiler.

Also note that, if you include a path separator in a #include directive, you must use a forward slash:

Slice
#include <SliceDefs/Clock.ice>  // OK

You cannot use a backslash in #include directives:

Slice
#include <SliceDefs\Clock.ice>  // Illegal

Detecting Ice Versions

The Slice compilers define the preprocessor macro __ICE_VERSION__ with a numeric representation of the Ice version. The value of this macro is the same as the C++ macro ICE_INT_VERSION. You can use this macro to make your Slice definitions backward-compatible with older Ice releases, while still taking advantage of newer Ice features when possible. For example, the Slice definition shown below makes use of custom enumerator values:

Slice
#if __ICE_VERSION__ >= 30500
enum Fruit { Apple, Pear = 3, Orange }
#else
enum Fruit { Apple, Pear, Orange }
#endif

Although this example is intended to show how to use the ICE_VERSION macro, it also highlights a potential pitfall that you must be aware of when trying to maintain backward compatibility: the two definitions of Fruit are not wire-compatible. 

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Detecting Slice Compilers

Each Slice compiler defines its own macro so that you can customize your Slice code for certain language mappings. The macro name is __<compiler name in upper case>__, such as __SLICE2CPP__ and __SLICE2MATLAB__ for slice2cpp resp. slice2matlab.


For example, .NET developers may elect to avoid the use of default values for structure members because the presence of default values changes the C# mapping of the structure from struct to class:

Slice
struct Record
{
    // ...
#if defined(__SLICE2CS__)
    bool active;
#else
    bool active = true;
#endif
}

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Definition Order

Slice constructs, such as modules, interfaces, or type definitions, can appear in any order you prefer. However, identifiers must be declared before they can be used.

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See Also