Preprocessor directives

The Slice compiler contains a preprocessor that can be used to conditionally compile parts of a Slice file.

Defining symbols

The Slice preprocessor relies on symbols that you define and undefine. The Slice preprocessor is much simpler than a C/C++ preprocessor; in particular, you cannot assign a value to a Slice preprocessing symbol.

#define DEBUG // defines symbol DEBUG
#undef DEBUG  // undefines symbol DEBUG

When defined, a symbol evaluates to true, and when not defined, it evaluates to false.

There is no difference between a symbol that hasn't been defined, and one that has been explicitly undefined. Additionally, it is safe to define a symbol that is already defined, or to undefine a symbol that is undefined, though doing so has no effect.

Conditional compilation

Conditional compilation allows you to include or omit sections of your Slice file at compile time, based on a set of boolean expressions.

It works just like a standard if-elif-else statement, but uses preprocessor directives:

#if <EXPRESSION_1>
    // this code is compiled when EXPRESSION_1 evaluates to true.
#elif <EXPRESSION_2>
    // this code is compiled when EXPRESSION_1 evaluates to false and EXPRESSION_2 evaluates to true.
#else
    // this code is compiled when both EXPRESSION_1 and EXPRESSION_2 evaluate to false.
#endif

You can also nest preprocessor directives. For example:

#if FOO
    //...
    #define BAR
    #if BAZ
        //...
    #else
        //...
    #endif
#endif

The #if and #elif directives require a boolean expression that the preprocessor evaluates. These expressions consist of symbols (which evaluate to true or false) and the following boolean operators:

• ! - Logical NOT
• && - Logical AND
• || - Logical OR
• ( and ) - Parentheses to group expressions

For example:

#if FOO && !(BAR || BAZ)
    //...
#elif BAR && BAZ
    //...
#endif