On Nov 16, 2008, at 9:22 PM, Zhongxing Xu wrote:
On Mon, Nov 17, 2008 at 1:14 PM, Zhongxing Xu
<[EMAIL PROTECTED]> wrote:
On Sun, Nov 16, 2008 at 12:27 PM, Zhongxing Xu
<[EMAIL PROTECTED]> wrote:
On Sun, Nov 16, 2008 at 11:28 AM, Ted Kremenek <[EMAIL PROTECTED]>
wrote:
On Nov 15, 2008, at 5:55 AM, Zhongxing Xu wrote:
One side problem is that I cannot make the MemRegion* in the
ImmutableList const. If I did that, I would get compile error,
related to FoldingSet Profile() overloading.
It seems that ImmutableList cannot take a const type as template
parameter, otherwise the two Profile functions in the partial
specialization of FoldingSetTrait would have the same signature.
(FoldingSet.h:444, 447).
Could we provide a partial specialization of FoldingSetTrait just
for ImmutableList? Or, does (something like) this work (i.e., add
another partial specialization for const types):
template<typename const T> struct FoldingSetTrait<const T*> {
static inline void Profile(const T* X, FoldingSetNodeID& ID) {
ID.AddPointer(X);
}
};
Yeah, this works! Thanks. Incidentally, do you think the old problem
is caused by a g++ bug, because, at FoldingSet.h:234, the parameter
for Add() already contains 'const', T should not contain 'const'
when being instantiated.
I was wrong. That was not g++ bug.
The template argument const T& need a const type. But const
MemRegion* is not a const type,
but a non-const pointer to const MemRegion. So T must match the
entire 'const MemRegion*'.
If T only matches 'MemRegion*', then the substituted type would be
'MemRegion* const', that is a const pointer to non-const MemRegion.
So if we write
template <typename T>
inline void Add(T const & x) { FoldingSetTrait<T>::Profile(x,
*this); }
that would be less confusing.
The problem is that we want a 'const MemRegion*' so that Profile()
operators on constant objects. If we had:
const MemRegion* R = ..
FoldingSetNodeID& ID;
ID.Add(R);
then (I don't believe) that this wouldn't work if we change Add() to
take a "T const& x" because it would require that the const qualifier
in 'const MemRegion*' to be cast way.
Is it possible to add a partial specialization just for pointer
types? e.g.:
<template const T*>
inline void Add(const T* X) { .... }
This seems simpler and also means that the pointer is passed-by-value
instead of passed-by-reference (which is less error prone)._______________________________________________
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