Most basic nothrow, pure, @safe functions?

[Walter Bright]

On 3/21/2014 11:23 AM, Steven Schveighoffer wrote:
> On Fri, 21 Mar 2014 14:18:05 -0400, Walter Bright <newshound2 at digitalmars.com>
> wrote:
>
>> On 3/21/2014 12:59 AM, monarch_dodra wrote:
>>> Ok. That's a fair point. So in that case, our function is pointing at "data",
>>> and is allowed to mutate it, and observe its state.
>>>
>>> Now, if *another* piece of code is doing the same thing at the same time
>>> (potentially mutating "data", does that still violate purity?
>>
>> A mutex essentially reads and writes a global flag, which other functions can
>> also read and write.
>>
>> That makes it NOT pure.
>
> No, that's not the case. A mutex does not write a global flag, it writes a
> shared flag. And the flag is passed into it.

Here's a litmus test you can use for purity. Consider:

     int foo() pure;
     {
	auto a = foo();
     }

Now, since 'a' is never used, we can delete the assignment, and since foo is 
pure, we can delete foo():

     {
     }

Is this program distinguishable from the former? If not, then foo() is not pure.