On 27/07/16 08:50, Walter Bright wrote:
On 7/26/2016 10:24 PM, Shachar Shemesh wrote:
Most D programmers, however, expect the program not to continue
executing past
an assert(false). They might see it as a bug. Hence my question
whether that
means D is not meant for programming in privileged mode.
Obviously, HALT means any instruction of sequence of instructions that
stops the program from running. Some machines don't even have a HLT
instruction. Do you want to make a stab at writing this for the spec?
Current text (after the strange copying corruption):
The expression assert(0) is a special case; it signi es that it is unreachable
code. Either
AssertError is thrown at runtime if it is reachable, or the execution is halted
(on the x86 processor,
a HLT instruction can be used to halt execution). The optimization and code
generation phases of
compilation may assume that it is unreachable code.
Proposed text:
The expression assert(0) is a special case; it signifies code that
should be unreachable. Either AssertError is thrown at runtime if
reached, or the assert message printed to stderr and execution
terminated. The optimization and code generation phases of the
compilation may assume that any code after the assert(0) is unreachable.
Main differences:
* Some phrasing improvements
* Change the confusing "is unreachable" (so why bother?) with "should be
unreachable", which stresses it's usefulness (and avoids the opinion,
expressed in this thread, that reaching it is UB)
* Remove the recommendation to use HLT on X86, which, as discussed, is
plainly wrong
* Define the behavior symptomatically, allowing both more certainty for
programmers relying on the specs to know what will happen, and for
compiler implementers more freedom to choose the correct way to achieve
this effect and handle resulting bugs.
* Add the requirement that the assert message be printed for assert(0)
Shachar
