Built-in functions

assert and panic, which every program can call without an import.

Source: runtime/internals.pep

assert

assert(condition: bool, message: String)

Panics with message when condition is false; otherwise does nothing.

The check always runs; there is no release mode that removes it. A string literal message picks the __ptr<char> overload instead, which builds no String. Any other message is evaluated before the call.

Parameters

• condition — the condition that must hold
• message — the text to print on failure; a null String prints a generic message

Panics

• if condition is false: prints the location and message, and aborts (see panic)

Example

assert(count > 0, "count must be positive");

assert

assert(condition: bool, message: __ptr<char>)

Checks that condition holds; if not, panics with message, a NUL-terminated C string. A string literal message picks this overload, so an assertion that holds builds no String.

Parameters

• condition — the condition that must hold
• message — the text to print on failure, or __null for a generic message

Panics

• if condition is false: prints the location and message, and aborts (see panic)

Example

assert(count > 0, "count must be positive");

panic

panic(message: String)

Prints message and aborts the program. It never returns.

Flushes every C output stream, so output printed so far is not lost, then writes location: panic: message and a newline to standard error (“Assertion failed with no additional information” when message is null), followed in a build without -O by a backtrace of the calls that led there (PEPPER_BACKTRACE overrides the build; see the debug module’s print_backtrace), and calls C abort(). No destructors or releases run, and the process ends abnormally (SIGABRT on POSIX).

The location is the call’s file:line:col, which the compiler passes in a hidden parameter, the way a C++ std::source_location default argument works. A function that panics on its caller’s behalf, as the runtime’s indexers do, declares that parameter itself and passes it on, so the panic names its caller’s line:

check_positive(value: int, location: __ptr<char> = __caller_location()) {
    if (value <= 0) {
        panic("expected a positive value", location);
    }
}

Parameters

• message — the text to print

Panics

• always

Example

panic("unreachable");

panic

panic(message: __ptr<char>)

Reports message, a NUL-terminated C string (a generic message when it is __null), as a panic and aborts, as panic(String) does. A string literal message picks this overload, so it allocates nothing.

Parameters

• message — the text to print, or __null

Panics

• always

Example

panic("unreachable");