Editing Defensive programming (section)

== Offensive programming ==
{{main|Offensive programming}}

Offensive programming is a category of defensive programming, with the added emphasis that certain errors should ''not'' be [[graceful degradation|handled defensively]]. In this practice, only errors from outside the program's control are to be handled (such as user input); the software itself, as well as data from within the program's line of defense, are to be trusted in this [[methodology]].

=== Trusting internal data validity ===

;Overly defensive programming
<syntaxhighlight lang="c">
const char* trafficlight_colorname(enum traffic_light_color c) {
    switch (c) {
        case TRAFFICLIGHT_RED:    return "red";
        case TRAFFICLIGHT_YELLOW: return "yellow";
        case TRAFFICLIGHT_GREEN:  return "green";
    }
    return "black"; // To be handled as a dead traffic light.
}
</syntaxhighlight>

;Offensive programming
<syntaxhighlight lang="c">
const char* trafficlight_colorname(enum traffic_light_color c) {
    switch (c) {
        case TRAFFICLIGHT_RED:    return "red";
        case TRAFFICLIGHT_YELLOW: return "yellow";
        case TRAFFICLIGHT_GREEN:  return "green";
    }
    assert(0); // Assert that this section is unreachable.
}
</syntaxhighlight>

=== Trusting software components ===

;Overly defensive programming
<syntaxhighlight lang="c">
if (is_legacy_compatible(user_config)) {
    // Strategy: Don't trust that the new code behaves the same
    old_code(user_config);
} else {
    // Fallback: Don't trust that the new code handles the same cases
    if (new_code(user_config) != OK) {
        old_code(user_config);
    }
}
</syntaxhighlight>

;Offensive programming
<syntaxhighlight lang="c">
// Expect that the new code has no new bugs
if (new_code(user_config) != OK) {
    // Loudly report and abruptly terminate program to get proper attention
    report_error("Something went very wrong");
    exit(-1);
}
</syntaxhighlight>