Source Code Fundamentals: Constants
A constant is a named value. Once defined, the value of the constant cannot be changed. A constant can be defined in one
of two ways: using the const keyword at the top level, or inside a class or
interface. For example:
const int MAX_COUNT = 123;
class C {
const float MAX_HEIGHT = 10.5;
const float UPPER_LIMIT = C::MAX_HEIGHT;
}
<<__EntryPoint>>
function main(): void {
echo "MAX_COUNT = ".MAX_COUNT."\n";
echo "MAX_HEIGHT = ".C::MAX_HEIGHT."\n";
}
MAX_COUNT = 123
MAX_HEIGHT = 10.5
Context-Dependent Constants
The following constants --- sometimes referred to as magic constants --- are automatically available to all scripts; their values are not fixed:
| Constant Name | Description |
|---|---|
__CLASS__ |
string; The name of the current class. From within a trait method, the name of the class in which that trait is used. If the current namespace is other than the default, the namespace name and "\" are prepended, in that order. If used outside all classes, the value is the empty string. |
__DIR__ |
string; The directory name of the script. A directory separator is only appended for the root directory. |
__FILE__ |
string; The full name of the script. |
__FUNCTION__ |
string; Inside a function, the name of the current function exactly as it was declared, with the following prepended: If a named namespace exists, that namespace name followed by "". If used outside all functions, the result is the empty string. For a method, no parent-class prefix is present. (See __METHOD__ and anonymous functions.) |
__LINE__ |
int; the number of the current source line |
__METHOD__ |
string; Inside a method, the name of the current method exactly as it was declared, with the following prepended, in order: If a named namespace exists, that namespace name followed by ""; the parent class name or trait name followed by ::. If used outside all methods, the result is the same as for __FUNCTION__. |
__NAMESPACE__ |
string; The name of the current namespace exactly as it was declared. For the default namespace, the result is the empty string. |
__TRAIT__ |
string; The name of the current trait. From within a trait method, the name of the current trait. If used outside all traits, the result is the empty string. |
Core Predefined Constants
Namespace HH\Lib\Math contains a number of integer-related constants (such as INT64_MAX and INT64_MIN).