Overview of Runtime Selection

Runtime selection lets one function contain different implementations for compile-time execution, native execution, and an alternate execution mode.

Compile-time and ordinary execution

The RUNTIME CONSTEXPR form provides separate implementations for compile-time evaluation and ordinary program execution:

::allocate TEMPLATE(@T TYPE AUTO) FUNCTION(): -> TYPED_STORAGE(T)
{
  RUNTIME CONSTEXPR
  {
    RETURN CONSTEXPR_ALLOC#T();
  }
  ELSE
  {
    RETURN allocate_native#T();
  }
}

The first block runs when allocate is being evaluated at compile time. The ELSE block runs during ordinary execution.

Native and alternate implementations

The RUNTIME NATIVE form isolates a native implementation:

RUNTIME NATIVE
{
  release_native(@address address);
}
ELSE
{
  release_portable(@address address);
}

If ELSE is omitted, the statement does nothing in the other mode.

Feature selection

RUNTIME chooses by execution mode. Ordinary IF evaluates a runtime condition. STATIC_IF evaluates a compile-time expression that determines which source body is generated.

Reference

For branch validity, dependency selection, variable state, and control-flow rules, see the Runtime Selection Reference.