On Saturday, 4 February 2017 at 14:33:12 UTC, Alex wrote:
Having read this https://dlang.org/spec/template.html#auto-ref-parametersI tried to do something like this // Code starts here void main() { initStruct iSb; iSb.var = 3; A b = A(iSb); assert(*b.myVar == 3); // this works iSb.var = 4; assert(*b.myVar == 4); // as expected b = A(initStruct(5)); // how does assert(*b.myVar == 5); // this work? } struct A { @disable this(); size_t* myVar; this()(auto ref initStruct iS) @nogc { import core.stdc.stdio;__traits(isRef, iS) ? printf("ref case\n") : printf("value case");myVar = &iS.var; /* // This treatment is not needed? if(__traits(isRef, iS)) { myVar = &iS.var; } else { myVar = new size_t(iS.var); } */ } } struct initStruct { size_t var; } // Code ends hereAll asserts pass. But the question is how it is possible to avoid the allocation of memory for the member var of the struct A in the second case. Is the input remains somewhere and I'm not aware of this? By the way, I find the fact very cool. I'm just wondering, whether I'm doing something unsecure...
It most likely only works because the dangling pointer points into yet untouched stack. Trying to öet a normal by-value parameter or local variable escape this way should produce an error, but apparently it's not done for `auto ref` parameters (the compiler should though, but only in the by-value-template-instantiation). So this isn't cool at all ;) - please consider filing a bugreport about this.
