purity question

[Brad Roberts via Digitalmars-d-learn]

On 5/28/2017 5:34 PM, Jonathan M Davis via Digitalmars-d-learn wrote:
> On Sunday, May 28, 2017 16:49:16 Brad Roberts via Digitalmars-d-learn wrote:
>> Is there a mechanism for declaring something pure when it's built from
>> parts which individually aren't?
>>
>> string foo(string s)
>> {
>>       // do something arbitrarily complex with s that doesn't touch
>> globals or change global state except possibly state of the heap or gc
>>       return s;
>> }
> <snip lecture> you can cast </snip lecture>
>

Ok, so there essentially isn't.  I'm well aware of the risks of lying to 
the compiler, but it's also not sufficiently smart to unravel complex 
code.  Combined with there being interesting parts of the standard 
libraries that themselves aren't marked pure, there's a real need for 
escape hatches.  A simple example: anything that has a malloc/free pair.