digitalmars.D.learn - is this a bug? opUnary!"++" Error: var has no effect
- Zach the Mystic (24/24) Feb 08 2012 My goal is to be able to overload the "++" operator transparently to the...
- Timon Gehr (6/30) Feb 08 2012 This is indeed a bug.
- Zach the Mystic (6/12) Feb 08 2012 Is that because has.myArc.opUnary!"++"() is going to be ignored at that
- Timon Gehr (9/25) Feb 08 2012 This is the issue:
My goal is to be able to overload the "++" operator transparently to the code, but I can't. import std.stdio; struct Arc { int I = 0; // This is void, but the error appears under all return types void opUnary(string op)() if( op == "++" ) { ++I; } } struct HasArc { Arc myArc; } void main() { HasArc has; writefln(" Arc.I = %s", has.myArc.I); // Arc.I = 0 has.myArc++; // Error: var has no effect in expression (__pitmp1481) // Okay, try this instead: auto UselessVar = has.myArc++; // Works fine writefln(" Arc.I = %s", has.myArc.I); // Arc.I = 1 } Obviously the expression has an effect. Bug? If not, what is the right way to have the "++" operator pass that error test? Thanks, Zach
Feb 08 2012
On 02/08/2012 10:48 PM, Zach the Mystic wrote:My goal is to be able to overload the "++" operator transparently to the code, but I can't. import std.stdio; struct Arc { int I = 0; // This is void, but the error appears under all return types void opUnary(string op)() if( op == "++" ) { ++I; } } struct HasArc { Arc myArc; } void main() { HasArc has; writefln(" Arc.I = %s", has.myArc.I); // Arc.I = 0 has.myArc++; // Error: var has no effect in expression (__pitmp1481) // Okay, try this instead: auto UselessVar = has.myArc++; // Works fine writefln(" Arc.I = %s", has.myArc.I); // Arc.I = 1 } Obviously the expression has an effect. Bug? If not, what is the right way to have the "++" operator pass that error test? Thanks, ZachThis is indeed a bug. The expression is rewritten internally into (pseudo code) (auto __pitmp1481 = has.myArc, has.myArc.opUnary!"++"(), __pitmp1481); This introduces a sub-expression with no effect. You may want to file a bug report. For now, just using ++has.myArc; should work around the issue.
Feb 08 2012
On 2/8/12 4:58 PM, Timon Gehr wrote:This is indeed a bug. The expression is rewritten internally into (pseudo code) (auto __pitmp1481 = has.myArc, has.myArc.opUnary!"++"(), __pitmp1481); This introduces a sub-expression with no effect.Is that because has.myArc.opUnary!"++"() is going to be ignored at that level of compiler activity? The compiler demands only that __pitmp1481 has a value at that point?You may want to file a bug report. For now, just using ++has.myArc; should work around the issue.http://d.puremagic.com/issues/show_bug.cgi?id=7467 Thanks, man. You're awesome!
Feb 08 2012
On 02/09/2012 12:47 AM, Zach the Mystic wrote:On 2/8/12 4:58 PM, Timon Gehr wrote:This is the issue: void main(){ int x; ++x, x; // error } While the whole expression has an effect, the single 'x' does not have an effect.This is indeed a bug. The expression is rewritten internally into (pseudo code) (auto __pitmp1481 = has.myArc, has.myArc.opUnary!"++"(), __pitmp1481); This introduces a sub-expression with no effect.Is that because has.myArc.opUnary!"++"() is going to be ignored at that level of compiler activity? The compiler demands only that __pitmp1481 has a value at that point?You're welcome. =)You may want to file a bug report. For now, just using ++has.myArc; should work around the issue.http://d.puremagic.com/issues/show_bug.cgi?id=7467 Thanks, man. You're awesome!
Feb 08 2012