Hi,
this is what happens:
while deducing a template match,
- a template instance of binaryFunImpl!false is created to evaluate
is(binaryFunImpl!(false).ReturnType)
- the template instance is added as a member to the module
- semantic analysis fails, so the respective startsWith alternative is
rejected
- compiler attempts to compile added binaryFunImpl!false and fails
so it helps to write
template binaryFunImpl(bool b)
if(b)
{
...
avoiding creation of the template instance, but I was not able to add a
similar test to startsWith in std.algorithm. Maybe someone else has an
idea how to do it?
Though this is kind of a blocker for me, should I add just add it as a
regression to bugzilla?
Rainer
Rainer Schuetze wrote:
Hi,
I've tried to untangle the startsWith code, and here's the minimal
test case I could come up with so far:
///////////////////////
template binaryFunImpl(bool b)
{
template Body()
{
static assert(b);
alias bool BodyType;
}
alias Body!().BodyType ReturnType; // line 9
}
uint startsWith(A)(A a) if (is(binaryFunImpl!(true ).ReturnType)) {
return 1; }
uint startsWith(A)(A a) if (is(binaryFunImpl!(false).ReturnType)) {
return 0; } // line 13
const uint var = startsWith(1);
///////////////////////
dmd produces:
test.d(6): Error: static assert (b) is false
test.d(9): instantiated from here: Body!()
test.d(13): instantiated from here: binaryFunImpl!(false)
The error does not show up if var is not const. Also, dmd 2.032 to
2.045 do not produce this error (2.046 fails), so it must be some
compiler regression.
As it seems, the compile time evaluation of startsWith uses the wrong
specialization. Maybe, it is just not gagging error output?
Any other ideas? I have not yet dived too deep into the template code
of the compiler, but if nobody has a better clue (and time), I can
give it a try.
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