Constly Const Pointer

语法糖

受不了了啊！指针与常量！别搁那“就近原则”了！来点从编译器视角的解析吧！

Define

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struct FRegirtry {
    int v = 0;
    void Set(int n) {v = n;}    // non-const method
    int Get() const {return v;} // const method
};
using FR = FRegistry;

Show me the memory

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FR r;
const FR cr;

r.Set(1);
r.Get();
// cr.Set(1);               // ERROR: cant set to const value
cr.Get();

r = FR();
// cr = FR();               // ERROR: cant use the Copy constructor

Just a ptr, inherit value’s constant feature

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FR* pr = &r;
// FR* pcr = &cr;  // ERROR: cant create mutable ponter to a constant value

pr->Get();
pr->Set(1);
// pcr->Get();
// pcr->Set(1);

pr = &r;
// pcr = &cr;

Constly ptr to a value, but ptr is not const

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const FR* cpr = &r;
const FR* cpcr = &cr;

cpr->Get();
// cpr->Set(1);  // ERROR: const ptr cant use non-const method
// cpr->c = 3;  // ERROR: an immutable left value
int c = cpr->c;  // OK: read as ref
cpcr->Get();
// cpcr->Set(1);

cpr = &r;  // OK: ptr object is not const :)
cpcr = &cr;

Const ptr to a value

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FR * const prc = &r;
// FR * const pcrc = &cr;  // ERROR: const ptr, but mutable to value

prc->Get();
prc->Set(1);
// pcrc->Get();
// pcrc->Set(1);

// prc = &r;  // ERROR: cant assign to a const value, btw its type is ptr
// pcrc = &cr;

Constly const ptr to a value

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const FR * const cprc = &r;
const FR * const cpcrc = &cr;

cprc->Get();
// cprc->Set(1);
cpcrc->Get();
// cpcrc->Set(1);

// cprc = &r;
// cpcrc = &r;
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