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# PetscUnreachable

Indicate to the compiler that a code-path is logically unreachable

## Synopsis

    #include <petscmacros.h>
    void PetscUnreachable(void)

## Note

Indicates to the compiler (usually via some built-in) that a particular code path is always unreachable. Behavior is undefined if this function is ever executed, the user can expect an unceremonious crash.

## Example usage

Useful in situations such as switches over enums where not all enumeration values are explicitly covered by the switch

      int foo(Color c)
      {
        // it is known to programmer (or checked previously) that c is either RED or GREEN
        // but compiler may not be able to deduce this and/or emit spurious warnings
        switch (c) {
          case RED:
            return bar();
          case GREEN:
            return baz();
          default:
            PetscUnreachable(); // program is ill-formed if executed
        }
      }

## See Also

`SETERRABORT()`, `PETSCABORT()`, `PETSC_ATTRIBUTE_COLD`, `PetscAssume()`

## Level

advanced

## Location

include/petscmacros.h

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