Example of Rust code

[Tove]

On Friday, 10 August 2012 at 12:32:28 UTC, bearophile wrote:
>
> This second D version uses the same class definitions, but 
> allocates the class instances on the stack. The code is bug 
> prone and ugly. The other disadvantages are unchanged:
>
>
> void main() {
>     import std.stdio;
>     import std.conv: emplace;
>     import core.stdc.stdlib: alloca;
>
>     enum size_t size_Val = __traits(classInstanceSize, Val);
>     enum size_t size_Plus = __traits(classInstanceSize, Plus);
>     enum size_t size_Minus = __traits(classInstanceSize, Minus);
>
>     Val e1 = emplace!Val(alloca(size_Val)[0 .. size_Val], 5);
>     Val e2 = emplace!Val(alloca(size_Val)[0 .. size_Val], 3);
>     Val e3 = emplace!Val(alloca(size_Val)[0 .. size_Val], 1);
>     Plus e4 = emplace!Plus(alloca(size_Plus)[0 .. size_Plus], 
> e2, e3);
>     Minus ex2 = emplace!Minus(alloca(size_Minus)[0 .. 
> size_Minus], e1, e4);
>
>     writeln("Val: ", eval(ex2));
> }
>
> Probably there are ways to improve my D versions, or to write 
> better versions.
>
> Bye,
> bearophile

I think version 2 would be the easiest one to improve, by 
including a combined emplace/alloca convenience function in 
Phobos for this common use-case.

See the technique used in:
http://www.digitalmars.com/d/archives/digitalmars/D/run-time_stack-based_allocation_166305.html

"auto Create(void* buf=alloca(frame_size))"