cppdraft_translate/cppdraft/conv/qual.md

[conv.qual]

7 Expressions [expr]

7.3 Standard conversions [conv]

7.3.6 Qualification conversions [conv.qual]

1

#

A qualification-decomposition of a type T is a sequence ofcvi and Pi such that T is “cv0 P0 cv1 P1 ⋯ cvn−1 Pn−1 cvn U” for n ≥ 0, where each cvi is a set of cv-qualifiers ([basic.type.qualifier]), and each Pi is “pointer to” ([dcl.ptr]), “pointer to member of class Ci of type” ([dcl.mptr]), “array of Ni”, or “array of unknown bound of” ([dcl.array]).

If Pi designates an array, the cv-qualifiers cvi+1 on the element type are also taken as the cv-qualifiers cvi of the array.

[Example 1:

The type denoted by the type-id const int ** has three qualification-decompositions, taking U as “int”, as “pointer to const int”, and as “pointer to pointer to const int”.

— end example]

2

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Two types T1 and T2 are similar if they have qualification-decompositions with the same n such that corresponding Pi components are either the same or one is “array of Ni” and the other is “array of unknown bound of”, and the types denoted by U are the same.

3

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The qualification-combined type of two types T1 and T2 is the type T3 similar to T1 whose qualification-decomposition is such that:

• (3.1)

for every i>0, cv3i is the union ofcv1i and cv2i,

• (3.2)

if either P1i or P2i is “array of unknown bound of”,P3i is “array of unknown bound of”, otherwise it is P1i, and

• (3.3)

if the resulting cv3i is different from cv1i or cv2i, or the resulting P3i is different from P1i or P2i, then const is added to every cv3k for 0<k<i,

where cvji and Pji are the components of the qualification-decomposition of Tj.

A prvalue of type T1 can be converted to type T2 if the qualification-combined type of T1 and T2 is T2.

[Note 1:

If a program could assign a pointer of type T** to a pointer of type const T** (that is, if line #1 below were allowed), a program could inadvertently modify a const object (as it is done on line #2).

For example,int main() {const char c = 'c';char* pc;const char** pcc = &pc; // #1: not allowed*pcc = &c;*pc = 'C'; // #2: modifies a const object}

— end note]

[Note 2:

Given similar types T1 and T2, this construction ensures that both can be converted to the qualification-combined type of T1 and T2.

— end note]

4

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[Note 3:

A prvalue of type “pointer to cv1 T” can be converted to a prvalue of type “pointer to cv2 T” if “cv2 T” is more cv-qualified than “cv1T”.

A prvalue of type “pointer to member of X of type cv1T” can be converted to a prvalue of type “pointer to member of X of type cv2 T” if “cv2T” is more cv-qualified than “cv1 T”.

— end note]

5

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[Note 4:

Function types (including those used in pointer-to-member-function types) are never cv-qualified ([dcl.fct]).

— end note]