Delay allocating class instance in stack.

[Ali Çehreli via Digitalmars-d-learn]

On 03/21/2017 01:08 AM, ANtlord wrote:
> void method(bool flag) @nogc
> {
>     scope MyClass obj;
>     if(flag) {
>         obj = new MyClass(1);
>     } else {
>         obj = new MyClass(2);
>     }
>     // using obj
> }

Another option is std.conv.emplace:

import std.conv : emplace;

class MyClass {
     this(int) @nogc {
     }

     ~this() @nogc {
     }
}

void method(bool flag) @nogc
{
     void[__traits(classInstanceSize, MyClass)] buffer = void;
     MyClass obj;

     if(flag) {
         obj = emplace!MyClass(buffer, 1);
     } else {
         obj = emplace!MyClass(buffer, 2);
     }

     // Unfortunately, destroy() is not @nogc
     // scope(exit) destroy(obj);
}

void main() {
     method(false);
     method(true);
}

Ali