dynamically allocating on the stack

[Timon Gehr]

On 21.04.2018 12:08, Giles Bathgate wrote:
> On Saturday, 21 April 2018 at 07:57:41 UTC, Uknown wrote:
>> The language itself doesn't have something, but you could use `alloca`
> 
> I don't know if this little template function makes life easier:
> 
> ------
> pragma(inline, true)
> ref T push(T)(size_t len)
> {
>      import core.stdc.stdlib, core.stdc.stdio;
> 
>      return *cast(T*)alloca(T.sizeof * len);
> }
> 
> 
> void doSomething(size_t len)
> {
>      auto stackBuffer = push!char(len+1);
>      stackBuffer[0] = 'H';
>      stackBuffer[1] = '\0';
>      printf("%.*s", stackBuffer.ptr);
> }
> 
> void main()
> {
>      doSomething(2);
> }
> ------
> 
> 

That does not work (you are returning a dangling reference into the 
stack of the function that is returning). You could do this:

import core.stdc.stdlib, core.stdc.stdio;
auto push(T,alias len)(T[] mem=(cast(T*)alloca(T.sizeof*len))[0..len]){
     return mem; // (uninitialized!)
}
void doSomething(size_t len){
     char[] stackBuffer=push!(char,len);
     stackBuffer[0] = 'H';
     stackBuffer[1] = '\0';
     printf("%s", stackBuffer.ptr);
}

void main(){
     doSomething(2);
}