Can a method definition specify that a parameter must be a constant?
+ (void) replace_text_with: (NSString *) const predefined_text_style;

typedef enum {
    FOOMy1stValue,
    FOOMy2ndValue,
    FOOMy3rdValue
} FOOEnum;

NSString *FOOGetStringFromEnum(FOOEnum e) {
    static NSString *strings[] = {
        @"My first value",
        @"My second value",
        @"My third value"
    };
    return strings[e];
}

void FOORestrictedInput(FOOEnum e) {
    NSLog(@"Restricted string: %@", FOOGetStringFromEnum(e));
}