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";
}
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 a defined, named namespace (not in root), 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 root 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).
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