Bug 832 – NRVO: return inside foreach results in junk

The behaviour changed in dmd-0.178 such that foreach on an array of structs only appears to do a shallow copy, rather than a deep copy. output of the code below is 29/30 or <.178, and a random number on 178/1.0. import std.stdio; const char[] XML_PUBLIC_ID_SYNCML_SYNCML11 ="-//SYNCML//DTD SyncML 1.1//EN"; struct WBXMLPublicIDEntry { int wbxmlPublicID; /**< WBXML Public ID */ char[] xmlPublicID; /**< XML Public ID */ char[] xmlRootElt; /**< XML Root Element */ char[] xmlDTD; /**< XML DTD */ } const WBXMLPublicIDEntry sv_wml11_public_id = { 33, XML_PUBLIC_ID_SYNCML_SYNCML11, "wml", "http://www.wapforum.org/DTD/wml.xml" }; struct WBXMLLangEntry { int langID; /**< Language ID */ WBXMLPublicIDEntry publicID; /**< Public ID */ } const WBXMLLangEntry mainTable[] = [ { 123, sv_wml11_public_id }, { 132, sv_wml11_public_id } ]; void main() { WBXMLLangEntry mt = getfirst(); WBXMLPublicIDEntry pie = getName(mt); writefln("got %d", pie.xmlPublicID.length); } static WBXMLLangEntry getfirst() { foreach(mt;mainTable) { return mt; } } WBXMLPublicIDEntry getName(WBXMLLangEntry mt) { return mt.publicID; }

Probably also NRVO-related. See http://d.puremagic.com/issues/show_bug.cgi?id=829 also.

> What |Removed |Added > ---------------------------------------------------------------------------- > Summary|Struct copying changed in |Struct copying changed in > |1.0 |1.0 Find the differences.. :S

// Smaller program with same problem. // Should print "1" three times, but only first is OK import std.stdio; struct Struct { int langID; long _force_nrvo; } Struct[1] table; Struct getfirst() { foreach(v; table) { //inout also doesn't work writefln(v.langID);// not OK return v; } } void main() { table[0].langID = 1; foreach(v; table) { writefln(v.langID);//OK break; } auto v = getfirst(); writefln(v.langID);// not OK }

For reference, the workaround is to return pointers to the struct, rather than passing around the Struct.

Tested both programs, work OK in 1.005

Fixed DMD 1.005

Added to DStress as http://dstress.kuehne.cn/run/s/struct_27_A.d