Variables and Constants in Tyhpdef

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Tyhpdef lets you describe existing PHP global variables and constants to the Tyhp compiler. This enables type-safe access to PHP superglobals, user-defined globals, and defined constants from your Tyhp code. You can specify types, alias names with as, and mark top-level imports deprecated or obsolete.

Declaring Variables

Variable declarations specify a type followed by the variable name. The compiler uses that type when your Tyhp code reads the global. There is no runtime existence check or ErrorException coercion generated from the tyhpdef.

<?tyhpdef

// Import a global variable with its type
string $globalAppName;

// Import an object variable
\App\Config $appConfig;

// Import a typed array
array<string, mixed> $globalSettings;

?? fallbacks (parsed, not applied)

The grammar accepts ?? after a tyhpdef variable or constant (int $maxRetries ?? 3). This alpha does not bind that default or emit isset / defined() / ErrorException checks. Treat ?? as reserved syntax: declare the type you actually use, and handle missing PHP globals in Tyhp/PHP yourself.

Variable Aliasing

Variables can be aliased using as $newName so your Tyhp code uses a different name than the PHP global.

<?tyhpdef

// Import $blah1 from PHP as $globalGuest in Tyhp
Guest $blah1 as $globalGuest;

Import by reference

Tyhpdef variable declarations do not accept &. int &$sharedCounter is not a tyhpdef form. Object values are PHP references as usual; scalars are whatever PHP already stored.

Declaring Constants

Constants are declared using the const keyword followed by the type and name. Constants are always immutable and globally accessible.

<?tyhpdef

// Simple constant declarations
const string APP_ENV;
const bool DEBUG_MODE;
const int MAX_CONNECTIONS;
const float PI_PRECISE;
const array<string> SUPPORTED_LOCALES;

Constant Aliasing

Constants can be aliased using the fully-qualified PHP name with as to use a different name in Tyhp.

<?tyhpdef

// Import PHP constant with a shorter alias in Tyhp
const int \MAX_LOOPS_ALLOWED as MAX_LOOPS;
const string \App\Config\DATABASE_URL as DB_URL;

Superglobal Type Declarations

PHP superglobals ($_GET, $_POST, $_SERVER, and similar) are typed by the tyhp/php package. You do not need to redeclare them unless you want a narrower project-specific type.

Deprecated and Obsolete

Both top-level variables and constants can be marked as deprecated or obsolete. Member-level markers on class constants are parsed but not enforced in this alpha.

<?tyhpdef

deprecated const string OLD_API_KEY;
deprecated string $legacyConfig;

Runtime Behavior

Tyhpdef imports are type information. The compiler does not emit existence checks, coercion, or ErrorException for missing globals. If a PHP variable or constant is unset, PHP's usual notices/errors apply at runtime.

Best Practices